The basic tenets of a face covering are fairly straightforward. “You want the mask to go over your nostrils and your mouth in such a way that it doesn’t slip off,” said Robin Patel, past president of the American Society for Microbiology. Even a bandana tied around your head is better than nothing. But if you want to maximize the potential protection to others and, likely, yourself, you might as well choose something more substantial. When you cough without a mask on, aerosols fly out of your mouth as far as about 8 feet on average, according to a June 2020 study. Tie on that bandana, and outgoing aerosols get only as far as 3 feet 7 inches on average, the authors found. Wear a well-fitted two-layer quilting-cotton mask, and those droplets, on average, stop short at a mere 2½ inches.
Although it’s true that some masks filter much better than others, a mask won’t help if it’s constantly slipping down your nose or it feels so suffocating that you’re forced to take it off. To find the best mask for you, focus on fit and comfort, and protection should follow (assuming you wear it properly, of course, and also practice social distancing whenever possible).
Fit: Creating a protective seal
For a mask to work to its fullest potential, it has to fit. “When there are large gaps for the droplets to come out, it doesn’t matter how good the filter is or how many layers you have,” said Linsey Marr, an aerosol scientist at Virginia Tech. As research at Northeastern University suggests, a mask that conforms closely to the face can enhance performance by as much as 50% over the same mask that doesn’t.
A properly fitting mask extends vertically from the bridge of your nose (just below the eye line) to about an inch under your chin, and it stretches horizontally from cheek to cheek, or even better, as close to your ears as comfortable. “Ideally, it should cover as much of your nose and mouth as possible,” said Grace Jun, an assistant professor of fashion and disability at Parsons School of Design in New York City.
Here’s what to do to make sure that happens:
Study the sizing chart. Masks are typically non-refundable; to ensure a reasonable fit, note a mask’s dimensions and then measure your face, including the inches added by any facial hair and the height of your nose, with a soft tape measure to confirm that the numbers correspond. (Some brands provide face measurements as opposed to mask measurements.) Note, too, that a pleated mask expands when you adjust it to cover your face. For instance, the height of the Rendall Co. Sentry mask we like is 3 inches pleated and 6½ inches expanded. When in doubt, ask customer service for detailed dimensions. If a mask is too short, it won’t stay put on your nose or chin. If it’s too tall, the edges can block your vision, poke your eyes, or hang too loose around your chin, said Jun. Too-wide masks can affect how the elastic fasteners fit around your ears or head. If your measurements fall in between designated sizes, size up and adjust the fasteners as needed, or better yet, look for another mask.
Don’t fall for “one size fits all.” That one size might not fit you. For example, the one-size-fits-all Banana Republic mask we like is 6 inches tall by 8½ inches wide, whereas the one-size-fits-all Hedley & Bennett mask is 6½ inches high by 9 inches wide. Among masks that come in multiple size options, not all size designations are created equal. “Even a quarter-inch can make a difference,” said Jun, especially if you have a wider or thinner face, a longer chin, or a higher nose bridge.
Look for a nose-bridge wire. A mask should gently hug the lines of your cheeks, dip along the sides of your nose, and curve over its bridge. A moldable wire helps a mask do that. Without that close fit, droplets can sneak in and out along the sides of your nose.
Consider the mask’s shape. Cone silhouettes are likely to curve to the cheeks better than a plain piece of cloth that lies flat or a rectangular mask with pleats does. That’s probably why the Northeastern University researchers have found that nylon-stocking seals often make less of a performance difference when layered over cone-shaped masks than when layered over masks of other shapes (though exactly how much of a difference may vary for different people; only one person took part in the study). “The fit was already good,” said study co-author Loretta Fernandez, an associate professor of civil and environmental engineering at Northeastern. Cone-shape masks have vertical seams that allow the fabric to “tent up,” giving it some height like a bra cup. Depending on the placement of the straps, cone-shaped masks can fit quite nicely on the cheeks.
However, masks with pleats provide more leeway for higher nose bridges, said Michael Kaye, who teaches draping and sewing as an adjunct professor at New York’s Fashion Institute of Technology. (He chose this pleated CDC-suggested pattern for his custom small-batch masks.) Compared with less generously cut cone masks, pleated masks may also feel more comfortable to some people because they allow for space between the fabric and your cheeks. (Read further for tips on improving the seal.)
Check for adjustable fasteners. A too-snug fit, one that leaves marks on your skin, may tempt you to take the mask off. For a secure fit, adjust any back-of-the-head elastic bands by either tying a knot or placing the band atop a ponytail. (Adjustments to the top band are especially crucial for helping the mask fit snugly around your cheeks.) Elastic ear loops with cord stops (such as those on the Banana Republic and Herschel Supply Co. masks we like) allow for a customizable fit. If you consistently find headband and ear-loop fasteners to be too tight, or if they get in the way of hearing aids, consider ties (as on the Rendall Co. mask we like); the drawback is that ties tend to loosen more easily over the course of the day.
Examine the fastener texture. Headbands with ridges can grip hair better without sliding, especially if your hair is straight, said Kaye. Ear loops made with elastic cords hang more easily on less-rigid ears but may make your ears feel sore after a few hours, especially if they’re too tight.
Comfort: Balancing breathability with filtration
Just the idea of something obstructing your nose and mouth can be distressing—hence the appeal of lightweight, single-layer masks made of more breathable fabric. But if your goal is to protect yourself as well as others, a well-fitting mask that balances breathability with filtration efficiency (the percentage of particles that a mask can block) works best, assuming you keep it on.
Protecting others is relatively easy: Almost any cloth can halt the larger-than-5-microns globules shooting from your mouth when you’re talking loudly, singing, coughing, or sneezing. But it’s snagging the 1-micron or smaller particles—which can come from you or others breathing and talking at regular volume—that’s tough.
Early in the pandemic, health officials considered those tiny aerosols to be less worrisome. But now experts believe that, in fact, such particles are also important to consider—with the smallest of them hovering in the air of a poorly ventilated room for hours, just waiting to be inhaled. In October 2020, the CDC published new guidance, recognizing that “COVID-19 can sometimes be spread by airborne transmission,” and that it’s possible to be infected in a poorly ventilated indoor space by a person more than 6 feet away or even shortly after an infected person has left the room. Timing also matters: According to the CDC, you’re more vulnerable to infection the longer you share air space with an infected person. Specifically, spending more than a cumulative 15 minutes over the course of 24 hours with an infected person constitutes “close contact.” (Independent experts have disputed the rationale behind both the 6-feet-of-distance and 15-cumulative-minutes-of-exposure guidelines, stating that even though the new guidelines are an improvement, droplets can infect others well over 6 feet away, depending on the ventilation, and this can happen in fewer than 15 total minutes.)
In December 2020, The New York Times reported that NIOSH has been collaborating with ASTM International (formerly the American Society for Testing and Materials) to develop standards for face mask fit, filtration, and breathability. As CDC/NIOSH health communication specialist Nura Sadeghpour explained, “products that don’t meet the standard may still have some utility, but won’t be able to claim that they meet the ASTM requirements, which provide a baseline for performance.” The new criteria are expected by April 2021.
In the meantime, many unknowns remain, including how much of the virus a person must inhale to cause an infection, said Sarah Brooks, director of the Center for Atmospheric Chemistry and the Environment at Texas A&M University. What’s more, no mask is guaranteed to provide complete protection. If you’re struggling to leave a mask on, play around with different materials. “You need to balance comfort and risk,” said Virginia Tech aerosol scientist Linsey Marr. To that end, consider the features below.
Tight weaves: Your mask is like a chain-link fence. “The more thread in a given area, the more solid the barrier, the harder it is to get through,” explained North Carolina State University textile scientist Bryan Ormond. As the aforementioned April 2020 study suggests, thread count (the number of vertical and horizontal threads in a square inch) matters. With droplets smaller than 0.3 micron at low flow (similar to what happens with breathing), a two-ply 80-thread-count quilting cotton exhibited far less filtration efficiency than a two-ply 600-thread-count pillowcase-like material. Unfortunately, few mask makers provide thread-count information online, and you’re left with taking their word for how “sturdy” or “tightly woven” the materials they’re using are. So before you buy, make sure your mask at least has multiple layers (read on), preferably with a filter pocket (see below). When the mask arrives, hold it up to the light. “The more visible openings you see in the fabric structure, the less effective the material may be at filtering particles,” Ormond said. To bolster a mask made with loosely woven fabric, add more layers in the filter pocket so as to block more of the light coming through (but not so much that the mask feels suffocating). Alternatively, you can wear a mask made with nonwoven materials underneath a cloth mask.
Multiple layers: According to a June 2020 meta review, multilayer masks are more protective than single-layer masks, and specifically “12–16-layer cotton masks” are associated with protection. (Insert laugh-cry emoji.) A more realistic goal, experts say, is to aim for a minimum of two layers: a somewhat water-resistant outer layer and a comfortable inner layer. A pocket for an additional middle layer, or filter, can be useful for higher-risk situations. “The mask is like an obstacle course for the virus to get through. Each layer can make a difference,” said Amy Price, a senior research scientist at Stanford’s Anesthesia Informatics and Media Lab.
Generous cut: This is the rare feature that enhances both breathability and filtration. By “generous,” we don’t mean a mask that’s too big for you. It should be a well-fitting mask that’s intentionally designed with a larger surface area so that it stands “taller” on your face (to allot more space between the fabric and your nose), wider on your face (with each side stretching closer to each ear), or ideally both. This way “you have more air coming through the cloth, and that air is filtered, as opposed to air sneaking in from the sides,” said Supratik Guha, a professor at the University of Chicago Pritzker School of Molecular Engineering, who co-authored the April 2020 study on mask materials. A simply cut flat mask creates the opposite situation: It sits close to your nose and mouth, so you have less filtered air to breathe in at any given time.
Filter pocket: Some masks, including those we like best, include at least two layers of cloth and a pocket that allows you to bolster your mask with an additional layer or two of your choice, whether it’s another piece of cloth or a sheet of nonwoven material. (Of course, you can also leave it empty.)
Nonwoven materials consist of fibers spun into a random web that is then heated to form a sheet. Slipped in between two or more fabric layers, the nonwoven material complicates the existing maze a virus needs to get through before it can reach your nose and mouth—creating “a tortuous pathway,” said Mark Losego, an associate professor in the School of Materials Science and Engineering at Georgia Tech.
There are almost as many nonwoven options being studied as cloth-face-mask filters as there are masks. Stanford’s Amy Price, who co-authored a June 2020 paper on the filtration efficiency of household materials, said that the polypropylene crafting material Oly-Fun can increase particle filtration efficiency by 10% to 20% per layer. This occurs with the help of electrical charging—rubbing it with a rubber glove—which makes that viral obstacle course even more challenging, at least for 24 hours, unless conditions are extremely humid, Price said. Paper towels and tissues can increase filtering capacity by 5% to 10% per layer (again, with electrical charging). A Texas A&M University paper currently under review (here’s the preprint) notes that non-fiberglass premium anti-allergen air filters—which, like Oly-Fun, also consist of polypropylene—seem promising. Some cloth-mask makers, such as Kitsbow, include their own removable nonwoven filter layers with their masks, along with the option to buy refills.
With research on non-medical mask filters’ efficacy and, in some cases, long-term safety still in its infancy, we can’t recommend the “best” filter just yet, though we hope to as the science accumulates. In the meantime, view any specific filtration claims with a healthy dose of skepticism. If you use one, try to find a filter that covers the entire expanse of the mask and stays put. Otherwise, you’re not taking advantage of the filter’s fullest potential—droplets tend to sneak through portions of a mask with the least resistance.