Masks Offer Covid Protection, Provided You Wear Them Right

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New research shows adding a filter and improving the fit makes a cloth mask work even better.

By Tara Parker-Pope

Is it time to upgrade your mask?

By now most of us have settled on a preferred cloth mask to protect ourselves and others from coronavirus. But new research shows that a few simple upgrades in fabric, filters and fit are likely to provide even more protection.

Linsey Marr, professor of civil and environmental engineering at Virginia Tech and one of the world's leading aerosol scientists, led the research, which tested 11 different mask materials. The findings confirmed what other labs have found: You don't need a gold-standard N95 medical mask to stay safe from coronavirus. The right cloth mask, properly fitted, does a good job of filtering viral particles of the size most likely to cause infection.

But Dr. Marr and her colleagues found that small improvements to your mask can go a long way toward improving how well the mask protects you and others from potential infectious particles. They found that:

Three layers are better than two. The best mask has two tightly woven layers of outer material with a filter material sandwiched in the middle, Dr. Marr said. You can use surgical mask material or even a piece of a vacuum bag as a filter between two pieces of fabric. Coffee filters are an option, but can be less breathable. If you like your two-layer mask, you can just wear it over a surgical mask when you want added protection. A well-fitting fabric mask with a third filter layer can stop 74 to 90 percent of risky particles, the researchers found.

Flexible material is better. Stiff material creates gaps. Look for a mask made of tightly woven flexible material that contours to your face. Masks with wire that can be molded around the nose also fit better by closing gaps where air can escape out and seep in.

Ties are better than ear loops. Masks that tie around your head fit better and can be more comfortable. Ear loop masks can leave bigger gaps around your face and cause ears to become sore with longer use.

Face shields should be used with a mask. Face shields alone offered little to no protection. Although the clear plastic shield is impermeable, air seeps out and comes in around the edges of the shield. "It was the worst of everything," said Jin Pan, a civil and environmental engineering Ph.D. student who was a co-author of the study. A face shield combined with a mask offers added protection, particularly for the eyes.

A well-fitted mask protects the wearer. Dr. Marr and her colleagues tested cloth masks for how well they protected others (outward protection) as well as the wearer (inward protection). Although masks are most efficient at filtering outgoing germs, they do stop incoming germs at nearly the same rate in most cases, the researchers found. Masks that did a poor job protecting the wearer were those made of stiffer materials and those worn loosely and with gaps around the edges.

A recent study from Denmark suggested that masks don't protect the wearer, but Dr. Marr noted that in that study, many people weren't using masks properly. "Fewer than half wore them as instructed," Dr. Marr said. Although Dr. Marr's findings come from a lab, rather than the real world, she said her group's latest research should offer reassurance to people who wear well-fitted masks that they are getting additional protection from other people's germs.

The research should also reassure people about the benefits of cloth masks, Dr. Marr said. She noted that masks can't do "100 percent of the work," and it's important to combine mask wearing with other measures, like hand-washing and restricting social contacts.

"Something is better than nothing," Dr. Marr said. "Even the simplest cloth mask of one layer of material blocks half or more of aerosols we think are important to transmission. If you go to a tighter weave and more layers, you’ll get even better performance."

The Virginia Tech study was published online and has not yet been peer reviewed.

Tara Parker-Pope is the founding editor of Well, The Times's award-winning consumer health site. She won an Emmy in 2013 for the video series "Life, Interrupted" and is the author of "For Better: The Science of a Good Marriage." @taraparkerpope

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