Is it time to update your mask?
In the meantime, most of us have chosen a preferred fabric mask to protect ourselves and others from coronaviruses. However, new research shows that some simple improvements to fabric, filters, and fit are likely to offer even more protection.
Linsey Marr, professor of civil and environmental engineering at Virginia Tech and one of the world's foremost aerosol scientists, led the research that tested 11 different mask materials. The results confirmed what other laboratories found: you don't need a gold standard N95 medical mask to be protected from coronaviruses. The right cloth mask that fits properly will filter out virus particles the size most likely to cause infection.
Dr. However, Marr and her colleagues found that small improvements to your mask can go a long way in improving the protection of the mask from 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 in the middle, said Dr. Marr. You can use surgical mask material or even a piece of a vacuum bag as a filter between two pieces of cloth. 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 for extra protection. A well-fitting tissue mask with a third filter layer can stop 74 to 90 percent of the risky particles, the researchers found.
Flexible material is better. Stiff material creates gaps. Look for a mask made of tightly woven, flexible material that molds to your face. Masks with wire that can be molded around the nose also fit better by closing gaps for air to escape and enter.
Ties are better than ear loops. Masks that tie around your head fit better and can be more comfortable. Ear loop masks can leave larger gaps in the face and lead to ear pain with prolonged use.
Face protection should be used with a mask. Face protection alone offered little to no protection. Although the clear plastic shield is impermeable, air leaks out and enters at the edges of the shield. "It was the worst of all," said Jin Pan, Ph.D. Student who co-authored the study. A face shield in combination with a mask offers additional protection, especially for the eyes.
A well-fitting mask protects the wearer. Dr. Marr and her colleagues tested fabric masks to see how well they protected others (external protection) and the wearer (internal protection). Although masks are most efficient at filtering out outbound germs, in most cases they stop incoming germs at nearly the same rate, the researchers found. Masks, which provided poor protection for the wearer, were made of stiffer materials and were worn loose and with gaps around the edges.
A recent study from Denmark found that masks do not protect the wearer, but Dr. Marr found that in this study, many people were not using masks properly. "Less than half were wearing them as instructed," said Dr. Marr. Although Dr. Marr's findings come from a laboratory rather than the real world, she said the latest research from her group should reassure people who wear well-fitting masks that they are getting extra protection from other people's germs.
Research should also reassure people about the benefits of cloth masks, said Dr. Marr. She noted that masks cannot do "100 percent of the work" and that it is important to combine wearing masks with other activities such as hand washing and restricting social contacts.
"Something is better than nothing," said Dr. Marr. “Even the simplest cloth mask made from a single layer of material blocks half or more of the aerosols that we consider important for transmission. Using a tighter fabric and more layers will give you even better performance. "
The Virginia Tech study was published online and has not yet been peer-reviewed.