The Best Air Purifier

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After carrying out 300 hours of research, three lab tests, and a weeklong real-world test encompassing 18 purifiers, all over the past four years, we’re more confident than ever that the Coway AP-1512HH Mighty is the best air purifier for most people.

Last Updated: This month
A new round of controlled lab testing and some real-world challenges in a New York City apartment confirm that our pick, the Coway AP-1512HH Mighty, is the best air purifier for most people. Our testing also helped us name a new budget pick in this update, the GermGuardian AC4825, a surprisingly good performer for about $100 or less upfront. New 2017 testing also confirmed that our other three picks (a runner-up, an upgrade pick, and an also great) remain the same.
Expand Most Recent Updates
One year ago: After a second, 80-hour round of intensive lab testing, our top pick remains the Coway AP-1512HH Mighty. It outperforms purifiers that cost far more, is the cheapest to own long-term, and maintains its performance for years—a Sweethome trifecta. Our new runner-up is the Winix 5500-2, a virtual copy of our to-be-discontinued former runner-up, the Winix Plasmawave 6300. For large spaces and/or people with severe particulate allergies, we have a new pick; the Coway Airmega 300 replaces the Blueair 503, whose performance collapsed during our two years of long-term testing. Finally, for odor/molecular-pollutant removal (on top of HEPA/particulate filtration), we’re sticking with our original pick, the Austin Air HealthMate Standard HM-400, whose best-in-class 15-pound activated-carbon sorbent filter outperformed all others.
One year ago: After a second intensive round of lab tests, our top pick for air purifiers is unchanged: The Coway AP-1512HH Mighty is the best for most people. It’s among the highest-performing and least-expensive HEPA-rated purifiers available, and is the least expensive to run and maintain for five years. Crucially, it also maintained its exceptional performance over the two years we’ve used it, exhibiting no falloff in particle filtration even while using the original filters. Our new runner-up is the Winix 5500-2, which performs similarly to our previous runner-up, the to-be-discontinued Winix 6300. For large spaces and/or people with acute sensitivity to particulate pollution, we have a new pick: the Coway Airmega 300. It replaces the Blue Air 503, whose performance dropped off precipitously over two years of use. For those with chemical sensitivity, our pick remains the Austin Air Healthmate Standard HM-400: Its 15-pound activated-carbon filter removes odors and VOCs better than any purifier we’ve tested. Finally, while “smart” purifiers are increasingly available, we’re not yet convinced they’re worth the price premium. Air purifiers are “always-on” and self-monitoring; there’s little need to monitor or control them from afar.
Two years ago: Thanks to a reader inquiry, we discovered an error in our guide. Our pick does not come with an extra carbon odor filter. We’ve updated the guide to reflect this.
Two years ago: Not content with lightbulbs, thermostats and locks, the Internet of Things revolution is looking to transform air purifiers as well. If you’ve ever been at work and become frustrated that you can’t check to see what the air quality is like at your house, this could be your year. We’ve added our notes about some of these new “smart” air purifiers below.
Two years ago: Both our main pick and runner-up choice are back in stock.
Two years ago: Our main pick and runner-up choice are both currently out of stock. If you need a new air purifier right away, we recommend you check out the Sharp Plasmacluster FP-A80U Air Purifier ($237) and Winix WAC5500 ($177). More details below.
Two years ago: Dyson announced it would add HEPA filters to its bladeless fan, the Pure Cool, enabling it to also act as an air purifier. The new Pure Cool will be available in China and Japan in April, but its availability (and price) in the U.S. and elsewhere is unknown right now. See the What to Look Forward to section for more detail.

Within 20 minutes—in the lab and in the challenging conditions of a New York City apartment—our pick reduced airborne particulate pollution by an average of more than 85 percent. And though it’s rated for spaces of 350 square feet, in 30 minutes it cut particulate pollution nearly in half in an apartment space almost twice that large. Simply put, it’s one of the highest-performing air purifiers we’ve tested. And it’s easily the most affordable. It not only outperforms purifiers that cost two and even three times as much upfront, but also costs far less to run and maintain for five years than any other purifier we’ve tested; you’re looking at about $600, including base price, replacement filters, and electricity. Finally, the Coway maintains its exceptional performance long-term: When we measured its performance using two-year-old filters—a year beyond their stated lifespan—it still cleaned the air almost like new.

Runner-up
Winix 5500-2
The Winix 5500-2 costs a bit more over time than our pick and isn’t quite as efficient over 20 minutes of purification—but it beats most others.

If the Coway is unavailable, the Winix 5500-2 is a close runner-up. It, too, is HEPA-certified and rated to 350 square feet. After 20 minutes of testing in the lab, it even slightly (albeit statistically insignificantly) outperformed the Coway, reducing particulate levels to 10 percent of their initial levels versus 12 percent for the Coway. We side with the Coway for proven long-term performance and lower long-term cost. The Winix costs about the same as the Coway upfront, but it is also a bit less energy-efficient and uses slightly more expensive filters. This means it will end up costing about $180 more (about $740 total) over five years’ operation. But if the Coway is unavailable and you need an air purifier ASAP, it’s a fine choice.

Upgrade pick
Coway Airmega 300
With a pair of filters, the Coway Airmega 300 is rated to clear spaces as large as 1,250 square feet and will keep smaller spaces exceptionally clean even on the lowest setting.

If you have severe allergies or other serious health issues related to airborne particles, or if you need to clean the air in a large space, we recommend the Coway Airmega 300. It’s HEPA-rated and designed to clear spaces of about 500 square feet at five complete air changes per hour (about 1.5 times the coverage of the Coway and the Winix at that level of air movement), or 1,250 square feet at two complete air changes. In our tests, the Airmega 300 and a slightly more powerful version, the 400, have consistently been at or near the top in terms of particulate reduction. Their unique twin filters permit very high airflow, allowing them to run on lower settings when the air is relatively clean or to rapidly filter very large volumes of air on the highest setting, as you might when allergens or pollution are elevated. But they are expensive; the 300 series costs about $1,200 (including the purchase price, electricity, and replacement filters) over five years—about double the cost of our pick.

Also great
Austin Air HealthMate Standard HM-400
A large activated-carbon filter removes most VOCs and odors, and a HEPA filter takes care of most particulates.

If you live in a problematic environment with high levels of both particulate and volatile organic compounds/molecular pollutants (such as near a farm where biocides are sprayed, a chemical/power plant, or a refinery), or if you are particularly sensitive to odors or other VOCs common in homes (like formaldehyde), we recommend the Austin Air HealthMate Standard HM-400. In our tests for odor/molecular removal, its 15-pound activated-carbon filter bested all other air purifiers by a wide margin. (Most air purifiers, including the other picks above, contain no or only token carbon filters and do effectively nothing to remove molecular pollutants—their strength is on particulate pollutants like fine dust). Its exceptional performance in this area is a big part of why FEMA and the Red Cross chose Austin Air units for deployment at Ground Zero and the surrounding areas in the aftermath of 9/11. That performance comes at a price, however: At about $1,350 over five years of use, it’s the most expensive machine we recommend; you could buy and run two Coway AP-1512HHs for less, and if particulates alone are your concern, that’s a much better deal.

Budget pick
GermGuardian AC4825
The GermGuardian AC4825 is a good performer at an attractive price, but it’s not as effective as our main pick when it comes to large spaces.

While our main pick (and our other picks) rated to 350 square feet or more, not everyone needs that sort of power—or the upfront cost associated with it. If you only wish to use a purifier in a bedroom, enclosed office, or a dorm room, the GermGuardian AC4825 is a decent choice. It costs about half as much as our main pick, with a price tag of less than $100. In the lab it reduced particulates by about 80 percent on average, and in our 200-square-foot NYC bedroom, it achieved a roughly 70 percent reduction on its highest setting (in comparison, our Coway pick approached 90 percent in both tests). But over five years’ use, the GermGuardian’s higher filter replacement and electricity costs make it more expensive than the Coway, so it’s only thrifty if you need a purifier in the short-term, or if (as in a dorm or office) you don’t pay the utility bill yourself.

Table of contents

Why you should trust us

John Holecek, who holds a master of science and is one of the guide’s researchers and a co-author, has conducted laboratory tests for Wirecutter’s air purifier reviews since 2014. Since 1999, he has studied particulate air pollution for the National Oceanic and Atmospheric Administration and in the private sector, in locations ranging from the continental US to the Arctic to the Maldives. Much of his government-sponsored research was aimed at improving our understanding of Earth’s climate by determining the sources, transport, and fate of airborne particles. John has also led research to develop aerosol particles with specific optical properties that produce a thick smoke cloud to protect soldiers from sensors and threats.

Tim Heffernan, guide editor, researcher, and co-author, has been at Wirecutter since 2015, and has comprehensively updated the air purifier guide annually since then. His formal education is in biology and economics. His journalistic expertise is in what you could call “big analog”—the physical machinery that runs our homes and industries, as opposed to “little digital” software and gadgetry.

Who should get this

Effective air purifiers can be expensive to purchase and operate. And despite the prolific marketing to the contrary, scientific studies do not support claims that they improve your health. That’s partly because it is exceptionally difficult to disentangle air-quality impacts from other environmental and genetic factors that influence health.

Balancing this is overwhelming medical and scientific evidence that breathing elevated levels of particulate pollution has serious negative health impacts, exacerbating asthma, allergies, and respiratory disease, and there is mounting evidence that particulate pollution is a cause of degenerative brain disorders, including Alzheimer’s and Parkinson’s disease. As if that wasn’t enough, exposure can increase mortality rates, especially among those with heart disease or compromised immune systems. Air pollution from US combustion emissions alone results in 200,000 premature deaths a year, according to a 2013 MIT study.

Then you have clear evidence that quality air purifiers are actually very good at their primary job, which is to remove particulate matter from the air—fine dust, pollen, mold spores, and so on. With that in mind, it’s less of a surprise to learn that air purifier owners offer extensive, almost universal testimony that the machines improve their sleep, reduce their allergies, and/or lessen their asthma symptoms.

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Go into this purchase with realistic expectations, though. Most of the filters you see don’t filter everything—as we explain in detail, most are HEPA-style filters that can’t catch nanoscale molecules like gases (radon, VOCs), and also can’t do anything about many allergens—dust mites and pet hair, for example—which sink and stick to furniture and other surfaces, and remain in the environment even after the air has been purified. To get rid of them, you’ll also need a good dust mop and/or vacuum cleaner.

Finally, no real-world home or office is remotely airtight; new particles are always being drawn in through windows, doors, ducts, and other openings. So air purification is a continuous process—and to be most effective, air purifiers need to run more or less around the clock. As the EPA says, “The best way to address residential indoor air pollution usually is to control or eliminate the source of the pollutants and to ventilate the home with clean outdoor air.” That means: Don’t smoke indoors, vacuum and dust regularly, and keep your pets outside when possible. Taking these measures alone will significantly improve your home’s air quality—if you want to go further, bring in an air purifier.

How we picked

For this guide, we focused on portable air purifiers, which is a blanket term for any purifier not installed directly into your home HVAC system—or, put another way, any purifier that can be moved from room to room. Several criteria guided our selection:

We required HEPA filtration. HEPA stands for High Efficiency Particulate Arrestance (or High Efficiency Particulate Air). HEPA means, in the US definition,1 that a filter removes 99.97 percent or more of airborne particles of 0.3 micron diameter. We go into detail on our thinking in How HEPA filters work. That section further distinguishes between basic HEPA products and another type of HEPA purifier that can also remove smaller pollutants that a standard HEPA filter would miss. We considered both types for the guide.

We focused on purifiers rated to clear spaces of at least 350 square feet—bigger than most living rooms. At this size rating, purifiers can keep most living spaces clean even on their more quiet, low-to-medium settings, and not need to blast on a noisier high setting all the time. However, new for 2017, we also tested an inexpensive purifier rated for spaces smaller than 150 square feet—basically, one made exclusively for a bedroom or office. Reader feedback suggested enough people would rather pay less upfront in exchange for a performance trade-off.

We believe the speed of purification is important. We looked for machines that can cycle all the air in a room at least twice per hour, and ideally four or five times—to measure this, we looked at the Clean Air Delivery Rate (CADR) standards assigned by the Association of Home Appliance Manufacturers. Our target was a 200+ CADR, which completely cycles the air in a 350-square-foot space about four times per hour.

We did not set a firm limit on price for air purifiers, but we did calculate their long-term ownership costs by factoring in the upfront investment, the cost of fresh filters over time, and their electricity consumption. These products are generally not cheap, but they tend to last a while, and the long-term approach helped us recommend ones that truly offer a good value.

We did not prioritize smart functionality, which, as in other technologies, is becoming more of a norm in air purifiers. For air purifiers, “smart” generally means they can give you more information and more control. Some can be monitored and adjusted remotely via a phone app; some can monitor a home’s air quality and send you updates on it. We don’t consider smart functionality a necessity, though, for two reasons. First, because our years of testing have proven that a good air purifier will create and maintain excellent air quality simply when allowed to run continuously on a moderate setting (versus letting the air quality, and the fan speed, fluctuate, as happens in smart modes). Second, because for now you often have to pay a premium for smart functionality, and while we could see the appeal, we don’t think you’re really getting enough for the extra cost.

Finally, we dismissed air purifiers that produce ozone to “purify” the air—and there are many that do. The theory is that ozone, a highly reactive form of oxygen, will “neutralize” or “break down” pollutants. Setting aside the dubiousness of that claim, even low levels of ozone can be harmful. It’s crazy to introduce a new pollutant when the goal is to reduce pollution overall.

With these standards and limitations in mind, over the course of four rounds of research (annually since 2014), we have surveyed hundreds of models from the Amazon best-seller list and big-box stores (Best Buy, Home Depot). We’ve read the reviews at Consumer Reports (subscription required) and at specialty air purifier sites including Allergy Buyers Club and Achoo Allergy. The extraordinarily detailed reviews at Air Purifier Power, written by Edgar V. Sherbenou, are some of the best anywhere. We also like Top Ten Reviews, which has a clean and easy-to-use website with informative content.

Based on this research and our ever-growing knowledge from years of evaluating purifiers ourselves, we’ve now selected and tested 18 air purifiers that met our initial standards and that have a track record of long-term performance, high professional ratings, and customer satisfaction. Among all of them, we are confident we have taken the full measure of what’s available, and what’s worthwhile.

How we tested

For 2017 we conducted two new tests of air purifiers. John Holecek re-created his 2016 lab tests in a new round of testing, including new models. Tim Heffernan did a week-long real-world test—the first of its kind that we know of—using Wirecutter picks and competitors in a New York City apartment.

The lab results give a measure of absolute performance under controlled conditions and act as a baseline for comparison of the air purifiers’ performance. The real-world results give something equally useful: a detailed picture of how our air purifiers performed in an everyday home (wool rugs, pollen, city air, a cat)—and, as it happened, in the middle of a stretch of hazardous outdoor air quality.

Both tests concentrated on particle filtration; John also measured VOC (molecular) filtration, noise levels, and ownership cost over time.

Between the two writers, they re-tested our longstanding main pick, the Coway AP-1712HH Mighty; our runner-up, the Winix 5500-2; and our pick for VOC removal, the Austin Air HM-400. We also tested five new purifiers:

Lab test details

Particulate pollution

John measured particle counts pre-, mid-, and and post-filtration, with professional-grade equipment used for atmospheric research (specifically a TSI Inc. 3080/3010 Scanning Mobility Particle Sizer and 3321 Aerodynamic Particle Sizer).

The tsi scanning particle sizer sitting in a laboratory.

The TSI Inc. 3080/3010 Scanning Mobility Particle Sizer is a specialized particle-test machine that counts individual particles as it scans across the size range from 0.01 to 0.50 micrometer. Photo: John Holecek

Drawing on his 12 years of experience measuring airborne particles, John used two sources to produce a dirty, particle-filled room: Combustion from four Diamond safety matches, to create small smoke particles (0.010–0.300 micron); and 55 milligrams of powdered titanium dioxide, commonly used to provide the white pigment in plastics and paints, to generate midsize particles (0.3–1.0 micron). This generated at least a 50-fold increase in particle concentration (to ~50,000 particles per cubic centimeter) over the background (~1,000 particles per cubic centimeter).

The test lab is 21 by 10 by 12 feet, with built-in lab equipment that reduces its effective size; adjusted to reflect the 8-foot ceilings found in a typical home, it’s equivalent to about 240 square feet—the size of a 12-by-20-foot living room. To minimize air entering and leaving the lab during his tests, John sealed the vents and weather-stripped the doors.

An air vent sealed using a garbage bag.

To minimize external interference on particulate levels, we sealed the testing-room vents and added weather stripping to the doors. Photo: John Holecek

Numerous burned matches sitting in a glass container.

The Hot Zone: Remnants of wooden matches used to produce fine smoke particles. Photo: John Holecek

In 2016 and 2017, John ran two or three baseline measurements on the particle concentrations in each room before running his tests. He then tested each unit three times, measuring particle concentrations in the air at 10 and 20 minutes, running the machines on their highest setting that produced sub-55-decibel (“conversational”) noise levels.

The graphs above show the test models’ absolute performance when measured against the initial particle concentration in the lab. In other words, they show the percent change each purifier achieved. This allows a direct comparison of their performance, by eliminating differences in initial pollution levels. Some key takeaways:

  1. Our pick, the Coway AP-1512HH Mighty, performed exceptionally well in 2016 and 2017. Even more important, it performed equally well using two-year-old filters and brand-new ones (see the 2016 test). So not only does it perform exceptionally when new—but also keeps doing so for years.
  2. The longer all of the purifiers ran, the more particulates they removed. That’s good, since most in the home typically run 24/7. None will ever achieve zero particulate pollution, since new polluted air is constantly entering homes through windows, doors, and vents. But even in our short, 20 to 30 minute tests, we saw differences in the rate of purification, an indication of how well (or poorly) a purifier is engineered.

Noise

Most air purifiers have three or four fan speed settings, and in terms of noise output, there’s typically a large jump when you switch a purifier to high. But 99 percent of the time you’ll run your machine on one of the low or medium settings. So John measured the noise produced by each machine on the highest middle-speed setting. He used the NoiSee app on a late-model iPhone, at a distance of 1 meter away and 0.5 meter above the ground, the standard for hi-fi speakers. (NoiSee is one of the top recommended apps in a survey of 192 apps by the National Institute for Occupational Safety and Health, where it came within +/-2 decibels of reference measurements. That’s plenty accurate for our purposes.)

We set 55 decibels, about the highest that would not interfere with normal conversation, as our limit; and we eliminated any machine louder than that on its moderate fan setting.

Molecular filtration

In 2014, John measured all of that year’s test purifiers for their effectiveness at removing VOCs, or molecular pollution. He added 5 milliliters of ethanol to a Pyrex dish heated to 50 degrees Celsius (122 °F), where it quickly evaporated, and used a fan to distribute the vapors through the test lab. He then measured the concentrations of ethanol vapor at the beginning (averaging about 35 parts per million), and again after 15 minutes of running the air purifiers at their highest moderate speed. (Test equipment was an RAE Systems miniRAE 3000 VOC meter.)

The results from the VOC testing were illuminating. While most air purifiers we tested claimed to be effective at removing VOCs, most had almost no impact, including the Coway AP-1512HH Mighty (our main pick). That’s because most use only a thin sorbent filter of activated carbon, alumina, and/or zeolites (a class of minerals with a unique physical form that means they can act as molecular filters). However, one model stood out: The Austin, which contains 15 pounds of activated carbon and zeolite, left only 13 percent of baseline ethanol remaining.

This 2014 test set a baseline for all our future tests: Any unit with less than 5 pounds of chemical adsorbent would likely fail the VOC/molecular-pollution test, so we mostly stopped conducting it. In 2017, however, we tested the updated Dyson Pure Hot + Cool Link for VOC removal, because the company claimed to have significantly improved its VOC filter. (See The competition part of this guide for details on it and other models.)

Cost

Both upfront and operating costs are a significant part of owning an air purifier. These units can be expected to last for several years, so we took a long view at the cost of ownership of our picks, including the purchase price, electrical consumption, and recommended filter replacement schedule, using the shortest time for filter replacement if a range was specified.

Make/Model

Purchase cost ($)

Annual filter cost ($)

Annual electrical cost ($)

5-year cost ($)

Austin Air HM-400 538 43 118 1,343
Coway AP-1512HH 230 50 25 605
Coway Airmega 300 455 99 49 1,195
GermGuardian AC4825 90 60 70 740
Winix 5500-2 160 80 27 695

2016/17 cost calculations. Purchase cost as of August 2017. Note: The Austin filter lasts five years, so the annual cost is calculated by dividing its price by five.

John measured the purifiers’ power consumption with a Sperry DSA-500 clamp-on ammeter. In the table above, calculations for electricity cost are based on the highest fan setting that didn’t exceed the 55-decibel noise limit. Electricity rates are based on residential rates in John Holecek’s area in 2016 (approximately $0.15396 per kWh) and 24/7 operation. (Rates vary state to state and city to city, of course, but California is in line with much of the country; the Northeast, the Mid-Atlantic, and the Pacific Northwest are generally higher. If you wish to calculate more accurately, see the latest state averages.)

Real-world test details

For Tim’s real-world tests, he pitted seven air purifiers against the New York City summer air. As it happened, the week he ran the tests was one of the worst, in terms of air pollution, of 2017, with temperatures in the high 90s and numerous health advisories related to outdoor air quality.

He measured the purifiers’ performance against particulate air pollution with a TSI Aerotrak 9306, a professional-grade handheld particle counter capable of measuring particles down to the HEPA-standard 0.3-micron size.

His “lab” was the back room of his Queens apartment. It’s approximately 200 square feet (18.5 square meters; 16 feet by 12.5 feet), with 8-foot-6 ceilings. The floor is hardwood but mostly covered with old wool rugs. There’s some wood furniture and a daybed with a wool blanket. The building is across the street from a well-planted city park and in the middle of a very leafy neighborhood. Elevated trains run past two blocks north and two blocks south, and two major thoroughfares—Queens and Northern boulevards—are just a few blocks farther. Big Alice, the city’s largest power plant, is a mile or so west; three highways, the BQE, the LIE, and the GCE, are a similar distance east, north, and south. He lives just outside the usual approach flightpath to LaGuardia International Airport. And he has a cat. Simply put: His apartment is a good place for testing particulate air pollution, from pollen, dust, and pet dander to soot and exhaust.

The week he ran the tests was one of the worst, in terms of air pollution, of 2017, with temperatures in the high 90s and numerous health advisories related to outdoor air quality.

He set each air purifier 18 inches from one of the long walls of the back room, about a third of the way from one end of the room. He set the particle counter 6.5 feet (2 meters) away, 90 degrees to one side of the purifier, about a third of the way from the other end of the room. This was to avoid any potential “halo effect” of cleaned air settling near the purifier and creating a false reading.

The blue TSI Aerotrak 9306 air quality tester sitting on a wooden table.

The TSI Aerotrak 9306 detects particles as small as 0.3 micron, which is the standard for HEPA certification. Photo: Tim Heffernan

Tim ran two tests on each purifier: a 20-minute cycle on the sub-55-decibel setting (medium/midrange on most machines), and a 30-minute cycle on the high setting. Each test consisted of 20 or 30 45-second sensing periods, separated by 15-second periods with the particle counter idling, in order to generate a minute-by-minute picture of how the purifiers were performing.

Immediately prior to each test, he took a 45-second reading on his balcony, to set an outdoor baseline, and another in the test room with the purifier off, to set the indoor baseline. He then turned on the purifier and left the room for the duration of the test.

Each morning, before any tests, he simply measured the particulate levels in the back room for 20 minutes, to get a baseline on how the room was “behaving” that day: Even in still air, particulate levels vary as particles clump together, settle on surfaces, or kick back up if someone (like a Wirecutter writer) walks past.

He did not attempt to hermetically seal the room—after all, we wanted to see how the machines performed in real-world conditions—but did take two steps to make it more like a typical home with central HVAC. Tim sealed off the through-wall air conditioner with foil and tape, in case of leaks around the perimeter—most homes don’t have large holes in their outer walls. And he closed the vents on his apartment’s two forced-air ventilation shafts, which draw about 200 cubic feet of air per minute out of the apartment—and a corresponding amount into it from outdoors. (Central HVAC, by contrast, recirculates the inside air.)

After the back-room tests were finished, he conducted two additional tests. First, on a handful of units (our main pick and the large-room models), to see how they performed when running on high in a large space (the 600-square-foot living room-kitchen-dining area-hallway), with the AC on and people moving around as they normally would. And second, on our main pick, to see how it performed overnight on low with the air conditioner blasting and a guest using the daybed in the back room.

As in the lab tests section above, these graphs show the test models’ absolute performance when measured against the initial particle concentration, but in Tim’s real world apartment. And again, they show the percent change each purifier achieved, allowing for direct comparison of purifier performance by eliminating differences in initial pollution levels. The key takeaways here:

  1. The first reading reflects the conditions of the air outside; the second reflects the air inside, prior to turning on the purifiers. You’ll notice that the air inside, in every case, is worse than what is outside. That’s counterintuitive, but typical: Inside air quality generally reflects the outside air conditions—and adds new sources of particulate pollution, like pet dander, dusty carpets and rugs, and people moving around and stirring things up.
  2. One of the Coway AP-1512HH high tests cuts off at 22 minutes, rather than 32. That was a mistake: Tim set the particle counter to the “recipe” for the low-speed, 22-minute test. But this didn’t alter the purifier settings, the readings, or the results, and as you can see, even with 10 fewer minutes to purify the air, the Coway gave one of the best absolute performances. Had it run for the full 32 minutes, it would have done even better. The other, full-length Coway high test—the red line with two prominent spikes—was a dry run. I kept it here to show how simply opening a door, which I did twice to check on the equipment, can cause air pollution levels to jump in a room. But more importantly, you can also see how quickly the Coway brought the pollution back down to less than 15 percent of the starting level—joint-best in the test.
  3. The Airmega 400 performed vastly better in the low-speed test compared with all of the others. Its exceptional performance likely results from a combination of factors: It (like the 300 series John tested in the lab) features a pair of HEPA filters, while the other machines use only one filter; and its sub-55-decibel setting is the third highest of its four speeds, while most others ran on their middle setting.
  4. The three “all apt” (all-apartment) tests reflect different conditions from the rest: Tim ran the Coway AP-1512HH, the Airmega 400, and the Austin Air HM-400 on high for 30 minutes in his combined kitchen-dining room-living room-hallway, a roughly 650-square-foot space. Also, the AC was on, and he and his cat were walking around. It’s noteworthy that the Coway—rated to barely half that square footage—nonetheless reduced particulate levels by about 50 percent.

Test conclusion

After four exhaustive rounds of testing spread across four years, we recommend five purifiers, in four categories: an overall top pick and runner-up, best for most people and most rooms; a pick for large spaces and extreme particulate pollution; a pick for extreme particle-plus-VOC filtration; and a new budget pick, best for small, enclosed offices or dorm rooms.

Our pick: Coway AP-1512HH Mighty

The Coway AP-1512HH Mighty air purifier set up in a grey and birch living room.

Photo: Michael Hession

After three tests in the lab, one in a New York City apartment, and three years of in-home use, we are more confident than ever that the Coway AP-1512HH Mighty is the best air purifier for most people. It’s one of the best-performing air purifiers we’ve ever tested, and beat some machines that cost three times as much; it maintains that level of performance over the years, whereas some others’ performance degrades; and its low upfront, maintenance, and electricity costs make it the cheapest to own of our main contenders.

The Coway is HEPA-certified and rated to clean areas up to 350 square feet—the size of a large living room, and far bigger than the average bedroom. In terms of measured particle removal, the Coway is very nearly the best we’ve tested. On the moderate setting—the highest you’re likely to ever run it on for long periods—it purified better than all but two units in our 2016 lab test, reducing particle concentration to just 12 percent of the background level after 20 minutes when set on medium/sub-55-decibel. (Of the two machines that bested it, one, our runner-up Winix, only beat it by a statistically insignificant 2 percent; the other, the Blueair 503, showed seriously degraded performance when we re-tested it after a year of occasional use, and we no longer recommend it; see The competition.) In the 2017 lab test, the Coway again shone against the competition, reducing particulates to as little as 10 percent of the initial level.

Just as important, the Coway showed virtually identical performance in our 2017 real-world test, reducing particulate pollution to less than 20 percent of the starting level in 20 minutes in a New York City apartment, when set on high—good for joint third best. It cut pollution by more than half in 20 minutes on medium/sub-55-decibel—second best in the test. The bedroom we tested it in is a challenging space, containing old wool rugs and years of pet dander, and located near a park (a big source of pollen), major roads, highways, and railroads, and the city’s largest power plant. Air quality in the city was deemed hazardous by the National Weather Service during our test, too.

The Coway also performed very well in our “large space” real-world test, reducing the particulate level by nearly 50 percent in a roughly 650-square-foot space (nearly twice its rated area) when set on high, and with an air conditioner running and a cat and a Wirecutter editor walking around. That’s better than the Austin HM-400, rated for large spaces like this one, and not much worse than the Airmega 400, which is rated for spaces as large as 1,500 square feet.

The Coway has also demonstrated the ability to maintain its high performance for years, even when pushed far beyond the stated lifespan of its filters. These, like most HEPA filters, are meant to be replaced once a year. We ran our original test model virtually nonstop for two years without replacing the filter—twice what’s recommended—and it still worked as well as it did on day one. That’s not hyperbole: In 2016 we measured its performance using both the original filters and brand-new filters, and there was no significant difference between them.

Opening the Coway revealed why it excels long-term. First, its prefilter does a stellar job of removing large particulate matter (pet hair, dust), leaving only fine particles to enter the HEPA filter. Second, its HEPA filter is beautifully sealed, with no leaks around the edges that could let fine particles skate through.

The Coway is easily the wallet-friendliest air purifier of its size-class (~350 square feet) that we’ve tested. To buy and run one 24/7 for five years will set you back about $600, or $120 a year. (Our otherwise comparable runner-up, the Winix 5500-2, will cost about $100 more (about $700 total) over five years; other similarly-performing purifiers we’ve tested over the years will set you back $1,000 or more. Another way to look at this is: You could buy and maintain two Coways for five years for less than the cost of some individual competitors. That’s not just a financial concern: Air purifiers perform best when cleaning a single room. So it’s worth considering separate machines for, say, the bedroom and the living room.

The Coway is quite small at 16.5 inches wide by 18 inches tall and 9 inches deep, about the size and shape of a large beach tote. Visually, it’s the least obtrusive machine we tested, with its simple shape, clean design, and low height. The Coway comes in either black or white, allowing you some flexibility in fitting it to your decor. And the Coway is light, just over 12 pounds. That makes it easy to move from room to room if that’s needed.

Finally, in addition to being extremely quiet on its moderate setting—51.1 decibels, where normal conversation averages 55 decibels or greater—the Coway is effectively silent on low, at 42.7 decibels. If you’re using it in a bedroom, a 15-minute cycle on medium or high will deeply clean the air before you go to sleep, after which keeping it on low will maintain very clean air all night—and produce no appreciable noise.

Flaws but not dealbreakers

One negative note: Like many air purifiers, the Coway has an ionizing function, which purports to introduce ozone to the air in your room as an additional “purifying” process. But unlike on some others, the function is user-controlled. We recommend leaving the ionizing function off. Its effectiveness is dubious, and ozone is a known component of degraded air quality.

One trend you see in the scant negative reviews on the product is a complaint about non-responsive customer service. However, as you see in this review of a malfunctioning unit, Coway responds in the thread. So, it may not be as easy to reach representatives as it should, but they are out there and listening—at least, to the negative public-facing reviews. Coway has an Austin, Texas-based support center; you can reach it at support@coway-usa.com or 1-888-960-5747.

Runner-up: Winix 5500-2

The Winix 5500-2 air purifier sitting on a brown carpet.

Photo: John Holecek

Runner-up
Winix 5500-2
The Winix 5500-2 costs a bit more over time than our pick and isn’t quite as efficient over 20 minutes of purification—but it beats most others.

If the Coway AP-1512HH Mighty is unavailable, the Winix 5500-2 is a close runner-up. It, too, is HEPA-certified and rated to 350 square feet—again, that’s bigger than most bedrooms and similar to many living rooms. In our 2016 lab test, it slightly—statistically insignificantly—outperformed the Coway, reducing particulate levels to 10 percent of their initial levels, versus 12 percent for the Coway. Given its solid performance and runner-up status, we did not re-test it in 2017, but expect it would have performed similarly to the excellent Coway.

We side with the Coway for proven long-term performance and superior long-term cost and aesthetics. The Winix costs about the same as the Coway upfront, but it’s also a bit less energy-efficient and uses slightly more expensive filters. This means it will end up costing about $180 more over five years’ operation—or $36 more annually. Physically, it’s a bit taller, and it only comes in black. But if the Mighty is unavailable and you need an air purifier ASAP, it’s a fine choice.

Upgrade: Coway Airmega 300

The Airmega 300 air purifier sitting on a brown carpet.

Photo: John Holecek

Upgrade pick
Coway Airmega 300
With a pair of filters, the Coway Airmega 300 is rated to clear spaces as large as 1,250 square feet and will keep smaller spaces exceptionally clean even on the lowest setting.

If you have severe allergies or other health issues related to airborne particles, or if you need to purify the air in a seriously large space, we recommend Coway’s Airmega 300. It’s a physically large (14 by 14 by 20 inches—think the size of a side table) but attractive machine and is HEPA-certified to clear spaces of roughly 500 square feet at five complete air changes per hour (about 1.5 times the coverage of the Coway AP-1512HH), or 1,250 square feet at two complete air changes. Its unique twin filters permit very high airflow, allowing it to run on lower settings when the air is relatively clean (quieter, less energy) or to rapidly filter very large volumes of air on the highest setting, as you might when allergens or pollution are elevated.

It’s a great machine for large, open rooms, but it is expensive to buy (usually roughly $450) and runs about $1,200 (including the purchase price) to maintain over five years. That price is the main reason it’s not our pick: In comparison, you could buy and run two Coway AP-1512HHs (our pick) for the same amount. Related point: If you’re thinking of going big with this model because you need to clean the air in two separate rooms (bedroom and living room, for example), buying an air purifier for each room is a better option.

In 2017, we also tested an Airmega 4002—a slightly more powerful but otherwise identical purifier (rated to 1,500 square feet at two air changes per hour, and 625 square feet at five air changes; the 300 is rated to 1,250/500 square feet respectively). The 300 and the 400 are standout performers on both the sub-55 decibel (level 3 of 4) and highest settings. On the real-world low-speed fan test, in particular, a 400 series machine easily bested all others by reducing the particulate load in a 200-square-foot room to less than 20 percent of the starting level in 20 minutes; the next best, our main pick, the Coway AP-1512HH, reduced the load to about 45 percent. It was the best performer in our large space” test, too, lowering particulate loads by more than 50 percent in 30 minutes in a 650-square-foot space (on high, with an air conditioner running and a cat and a Wirecutter editor moving around, stirring up dust and dander).

Both the 300 and 400 have an otherwise identical smart model (designated by an S after the model number) you can control and monitor via a smartphone app. The filters and fans are the same—we actually used S-series units in our tests, but set them on their “dumb,” manual-control modes (as in the plain 300 and 400 models)—but the smart models offer the ability to remotely observe the air quality in your home and adjust the settings via an app. They can also automatically adjust the fan speed to address changes in air quality. But they come at a price premium of about $200 over the base 300 (our upgrade pick) and 400, and since the machines we tested performed exceptionally well when we simply ran them at a manually fixed speed—no matter how bad the initial air quality was—we think they’re right for most people.

Coway has an Austin, Texas-based customer-support center for the Airmegas: info@airmega.com and/or 1-800-285-0982.

Also great: Austin Air HealthMate Standard HM-400

The Austin Air purifier on a white background.

Photo: Austin Air

Also great
Austin Air HealthMate Standard HM-400
A large activated-carbon filter removes most VOCs and odors, and a HEPA filter takes care of most particulates.

In our tests for VOC/odor/molecular-pollution removal, the Austin’s 15-pound activated-carbon filter bested all other air purifiers by a wide margin. It reduced a heavy load of ethanol vapors to 13 percent of the starting point within 20 minutes; the nearest competitor did only half as well, and the rest were marginally or completely ineffective. (Most air purifiers, including the other picks above, contain no or only token VOC filters, and do effectively nothing to remove molecular pollutants). Its exceptional performance in this area is a big part of why FEMA and the Red Cross chose Austin Air units for deployment at Ground Zero and the surrounding areas in the aftermath of 9/11.

When it comes to particulate pollution, the Austin is a very solid performer, reducing particulates to less than 20 percent of starting levels after 30 minutes on high in our real-world test—fourth-best in our high-setting test—and to 50 percent, joint third-best, on low. But it’s not as fast or efficient as our pick; the dense carbon filter means the machine works slower and consumes more electricity. In fact, its electrical consumption is more than double all but one of our picks.

And its performance comes at a steep price: The Austin HM-400 typically costs more than $500, and replacement filters cost a bit more than $200. That said, the filters are designed to last five years, which works out to about $43 a year—and after five years, we figure the total cost of the Austin (with electrical use) to be about $1,300, roughly double the price of our pick and closer to the price of our upgrade pick.

The Austin is a very simple machine. It does not have a self-monitoring function, let alone smart capability; you have to pick and set your fan setting manually. Basically, it’s a room fan with a filter attached. And it’s a bit louder than most purifiers, producing an audible though not unpleasant fanlike white noise even on low.

If you simply need to remove particulates from your air in a large space, the Airmega is easier to live with, which is why it’s our main pick for large spaces and challenging environments. If you have specific concerns over VOCs, however, the Austin Air HM-400 is by far the best portable air purifier we’ve ever found.

Budget pick: GermGuardian AC4825

The GermGuardian AC482 air purifier sitting in a grey and white living room.

Photo: Michael Hession

Budget pick
GermGuardian AC4825
The GermGuardian AC4825 is a good performer at an attractive price, but it’s not as effective as our main pick when it comes to large spaces.

While our pick (and our other picks) are rated to 350 square feet or more, not everyone needs that sort of power—or the higher upfront cost associated with it. If you only need to use a purifier in a bedroom, small office, or a dorm room, the GermGuardian AC4825 is a decent choice. Usually priced less than $100 (versus $185 to $225 for our main pick, the Coway AP-1512HH), it’s both exceptionally popular—Amazon’s number one seller among purifiers, with 4.3 stars, 6,600-plus reviews, and a “trustworthy” rating from Fakespot—and a surprisingly good performer in our lab and real-world tests. In the lab, it reduced particulates by about 80 percent on average, and in our 200-square-foot NYC bedroom, it achieved a roughly 70 percent reduction in 30 minutes on its highest setting (compared with approximately 87 percent by the Coway in both tests).

However, there’s a big caveat: The GermGuardian is not cheap to run long-term. Replacing the filter on the recommended six-month cycle means an annual outlay of about $60—$100 more than the Coway. And compared with the Coway, it’s a power hog, consuming about $70 in electricity a year, versus about $21. With the purchase price included, that adds up to about $740 over the course of five years’ use, or $180 more than the Coway’s five-year cost. In short: over time, the upfront savings on the purchase price are outweighed by the higher maintenance costs. That’s not necessarily a dealbreaker; spreading costs over time is often wise. But the GermGuardian is only a true bargain if you need an air purifier for a limited time (say, in a temporary apartment), or if you don’t pay for your electricity—if you’ll use it in a dorm or work office, for example.

Finally, a note on the name: We doubt the GermGuardian can actually guard against germs. Viruses and bacteria are far smaller than the micron-scale particulates that it (and other HEPA filters) capture. It does employ a UV light to theoretically kill pathogens—contributing to its high power consumption—but according to the EPA, home UV air purifiers “have limited effectiveness in killing bacteria and molds. The effective destruction of some viruses and most mold and bacteria spores usually requires much higher UV exposures than a typical home unit provides.” If you’re worried about germs, you’re better off using proven methods like alcohol-based hand sanitizers.

The competition

We tested two tower-style units in 2017, the Coway AP-1216L and LG AS401WWA1 Puricare. Despite decent to solid performance, we don’t recommend either. Their small footprints (11 by 11 inches for the LG, 10 by 8 inches for the Coway) belie the fact that they’re 30 and 32 inches tall, respectively—as tall as a kitchen counter—and so they take up a huge amount of visual space. You’ll never forget that you have one in the room. And at about $500 upfront, the LG in particular doesn’t justify its cost.

The Coway Airmega 300S is the smart version of the Airmega 300 we recommend. It offers the ability to monitor your home’s air quality remotely via a smartphone app, and to manually adjust the fan speed accordingly. It also has a setting that lets the machine automatically monitor and adjust the fan speed according to air quality. This said, the 300S—and the Airmega 400S, the smart version of the slightly more powerful/larger-space Airmega 400 series—come at a price premium of about $200 over their base version. If remote monitoring is something you need, they’re worth considering. Just be aware that the filters and fans themselves are identical to the base versions—in terms of purification, they perform the same way—and our years of testing have shown that leaving a high-quality air purifier, like any of our picks, on a low or moderate setting will create and maintain excellent air quality without any need to monitor or adjust their operation.

In 2017, we also tested the Dyson Pure Hot + Cool Link for particulate performance in the lab and in the real-world New York apartment. It offers two distinct fan functions, diffuse and focused; we tested it on both functions in the lab and in the real world. John further tested the Hot + Cool Link for VOC removal in the lab, given that Dyson received an upgrade of its VOC filter since our 2016 test of its predecessor. In every case the Dyson delivered disappointing performance relative to our pick. On particulates, it proved considerably less effective, reducing particulates by roughly 25 or 50 percent (low and high fan settings respectively), versus 50+ to 85+ percent from other models. And as a VOC filter, it barely reduced the pollution level beyond the background conditions: to 34.7 parts per million (of vaporized ethanol) in 15 minutes on the highest fan speed, versus the 36.7 ppm background level over the same timeframe—a 5 percent reduction. Compare that to our pick for VOC removal, the Austin Air HM-400, which achieved an 87 percent reduction in our 2014 lab test. It’s only fair to note that the Dyson is a unique machine, combining the functions of a fan, a space heater, and an air purifier—both HEPA (particulate) and VOC (molecular)—no other purifier we tested attempts this broad utility. But the Dyson Pure Hot + Cool Link objectively underperformed simpler, single-function air purifiers that also cost much less. Given its high upfront cost and relatively weak performance, we can’t recommend it.

In every case the Dyson delivered disappointing performance relative to our pick.

Molekule is a new air purifier for 2017. Largely and successfully crowdfunded, it has received generally credulous press coverage (like this in The Verge) and generated a lot of public interest. Unlike virtually all other air purifiers—and all we’ve tested—Molekule is not HEPA-rated and does not claim to eliminate micron-scale particulates with a filter. Instead it claims to remove smaller, nanoscale pollutants, including VOCs and viruses, via a chemical3 rather than a physical process. Out of curiosity, we requested a model for testing for VOC reduction, but Molekule requested conditions around the testing that we could not agree to.

The QuietPure Home, a smart model in our 2016 test, had an easy-to-configure app but gave notably inferior performance compared with the otherwise comparable Coway Airmega 300.

The Blueair 503 was a standout performer in 100 hours of testing in 2014, and we recommended it with the SmokeStop filter package for people with severe health concerns tied to particulate air pollution. But it suffered a four-fold loss of particulate filtration when re-tested in 2016, using both the original filters and brand-new filters. Neither the manufacturer nor our own investigations were able to explain this (though at the maker’s request we sent the 503 back to the manufacturer for analysis; we have not yet received a report). And a thorough cleaning of the machine didn’t fix it. At well over $2,300 for purchase and five years’ maintenance—by far the highest in our 2016 test—that’s not acceptable.

In 2016, the Blue Pure 211 was a similar standout, dropping particulates to 3 percent of their initial concentration within 20 minutes, versus 11 percent for our pick, the Coway Mighty. Blue, however, is a subsidiary of Blueair—and the Blue Pure 211 uses the same technology as Blueair 503. The Blueair’s performance collapsed over the course of just two years of use, and remained poor even after replacing the HEPA filters and cleaning the machine thoroughly. Given that the Blue Pure 211 is made by the same company and utilizes the same technology, we can’t recommend either the Blueair 503 or Blue Pure 211.

The IQAir HealthPro Plus proved middling on both particulate and odor/molecular-pollution removal in our 2014 test, and it’s incredibly expensive to buy and operate—more than $3,000 over five years as we calculated in 2016.

The Rabbit Air MinusA2 SPA-700A earned middling performance, cost-of-ownership, and noise marks in our 2014 test.

The Rowenta PU6020 did not stand out on particulate filtration. It employs a unique formaldehyde-trapping filter, but those with chemical sensitivity should look to the Austin Air for broader odor/molecular-pollution removal. It’s also pricey to buy and run.

The Sharp Plasmacluster FP-A80 performed well on particulates in our 2014 test, but didn’t live up to its claims of molecular/odor removal due to its small (~1 pound) sorbent filter. That plus its high long-term cost (about $900 over five years) puts it in that unhappy middle ground of too much cost and not enough performance relative to true molecular/odor purifiers.

The Winix HR1000, a smart model in our 2016 test, has an easy-to-use app but gave unimpressive particulate-filtration performance at a relatively high cost—almost $1,000 over five years.

How HEPA filters work

HEPA stands for High Efficiency Particle Arrestance. The technology is the result of an industrial need that became critical in the aerospace age: high volumes of very clean air, vital for the production of microprocessors and other sensitive instruments. Happily, HEPA filtration is also fundamentally simple and cheap, which means it’s available to everyone today.

HEPA filtration is a physical process: It relies on momentum to capture variously sized microscopic particles when they’re drawn at high speed through a dense, feltlike net with gaps of varying size. It’s not that any given gap in the net’s mesh is fine enough to capture everything; it’s that, cumulatively, almost nothing but air will make it through the thick, multilayered net without being caught. That’s opposed to what most of us envision when we think of filtration: uniform particles (say, pieces of pasta) trapped by uniform holes (a colander) as the carrying medium (water) slowly drains away.

In HEPA filtration, a dense and seamless sheet of very small fibers (usually fiberglass) is pleated like an accordion and mounted, sealed at the edges, in a frame of metal or plastic, creating an airtight filter. A fan draws air rapidly from one side of the filter to the other, and the seamless sheet and the sealing mean that air on one side can’t pass through to the other side without being filtered. (To help ensure a steady airflow, many HEPA filters also interleave the pleats with impervious sheets of aluminum or plastic.)

The fibers in a HEPA filter capture airborne particulates in three basic ways, but they all come down to the comparatively huge differences in size between those particulates—solid, though generally microscopic, things like smoke particles—and truly infinitesimal gaseous atoms and molecules. The latter are so small that they flow more or less freely between the HEPA filter’s fibers, allowing for unimpeded passage of gases (“air”) from one side of the filter to the other. By contrast, particulates, while small on a human scale, are hundreds or thousands of times larger than gaseous atoms and molecules. That means particulates have so much momentum that they cannot simply “go with the flow” of the air. Instead, for three reasons, based on their size, they are pretty much guaranteed to slam into the fibers. In short, gases are drawn through quickly and with little resistance while, simultaneously, almost everything that isn’t gaseous gets caught. Thus, High Efficiency Particle Arrestance.

The largest of the particulates—those roughly the same diameter of or wider than the filter fibers, about 0.5 micron and above—are captured via impaction: Unable to change their course due to momentum, they simply slam into the fibers and stick to them. Particles less than the diameter of the fibers, but not too much less, are captured by interception: They “try” to flow around the fibers but come close enough to touch the fibers on the way by, and again stick. Finally, very fine particles— those below 0.1 micron, or one-fifth or less the diameter of the fibers—get bounced around randomly and slowed by their interactions with atmospheric atoms and molecules, and eventually drift or get bounced into a filter fiber, whereupon (yet again) they get stuck—a process called diffusion. The net result is that virtually all particles get captured.

Crucially, the hardest particles to capture are what you might call the Baby Bears: at 0.3 micron, they’re at the low limit of interception momentum and above the limit of diffusion—in other words, “just right” to get through a HEPA filter. The solution is to make the filter dense enough that even at the 0.3-micron limit, there are enough fibers between the unfiltered and filtered side to capture most of them. And again, according to the US HEPA standard, “most of them” means 99.97 percent—damn near all. Which is the standard we used. The European Union certifies HEPA on a numeric scale, and the lowest, and very common, one is less than 85 percent of 0.3-micron particles (“E10”). At the risk of offense: Buy American. And if you have to buy European, insist on a purifier rated to H13 (99.95 percent of 0.3-micron particles removed).

Footnotes:

1. The EU definition sets that number as low as 85 percent—more than three orders of magnitude less stringent. Jump back.

2. We requested a 300 series, but Coway sent a 400 series instead. The main difference is the 400 is rated for a larger space. We kept it for the sake of comparison against our two years of test results with the 300.
Jump back.

3. Molekule advertises its technology as PECO—photo-electrochemical oxidation. It is a variant of photocatalytic oxidation, or PCO, which came to prominence in the 1990s, as a way of eliminating ethylene—a ripening agent naturally produced by fruit—in cold-storage fruit warehouses. In the early 2010s, a PCO home purifier, the Airocide, was introduced to great fanfare but deeply dubious results. Molekule’s PECO variant is 15 to 100 times faster than what we’ve seen before, but Molekule says (in our lengthy interviews and in its own literature) that the fundamental chemistry is similar if not identical. Jump back.

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