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The Best Face-Mask Filters, According to Doctors and Scientists

Photo: Mike Coppola/Getty Images

Along with getting vaccinated, regular mask wearing is one of the best ways to protect yourself and others from contracting COVID-19, especially now that case numbers are soaring to record highs because of the Omicron variant. N95 respirator masks, certified by the National Institute for Occupational Safety and Health to filter out 95 percent of airborne particles, are the gold standard in virus prevention. Early in the pandemic, these masks were in short supply and generally reserved for health-care workers, so the public was advised to use less-effective cloth masks instead. Fortunately, N95 masks (and their Chinese equivalents, KN95s) are now more widely available, and these are what you really should be wearing. If you’re in a pinch or still having trouble finding an N95, you can boost your cloth mask’s efficacy by adding a filter.

In the same way that fit is critical when selecting a face mask, when possible, you should look for filters specifically designed for your mask. As Christopher Zangmeister, a researcher at the National Institute of Standards and Technology who tested 32 face-mask materials in one study, explains, air — and the respiratory droplets it contains — will seek out the path of least resistance and escape through the parts of your mask not covered by a filter. He compares wearing a filter not designed for your mask to putting your thumb over a hose: The water will escape through the areas not covered by your finger.

We asked Zangmeister and three other experts to tell us about the most popular filter options available online.

PM2.5 filters

These filters are designed to filter particles down to 2.5 microns in size. This is larger than the size of a free-floating coronavirus particle, but when you consider that the virus is usually contained in larger particles of saliva, salt, and proteins, it’s within that range. Dr. Krystal Pollitt, an assistant professor of epidemiology at the Yale School of Public Health, explains that because masks are generally more effective when they have more layers, a PM filter will add protection. Unlike masks, filters are not reusable and should be replaced roughly every 12 hours (which could be a few days of wear if you’re only using your mask for quick errands).

Figs, which also makes stylish and functional scrubs for health-care workers, sells PM2.5 filters that’ll fit in their masks and need to be replaced after 12 hours of wear.