The Best and Worst Materials for COVID-19 Masks

A recent study from the University of Arizona assessed the ability of a variety of nontraditional mask materials to protect a person from infection with coronavirus disease 2019 (COVID-19) after 30 seconds and after 20 minutes of exposure in a highly contaminated environment.

Researchers compared wearing masks with wearing no protection for 20-minute and 30-second exposures to COVID-19. The method showed that infection risks were reduced by 24% to 94%, or by 44% to 99%, depending on the mask type and exposure duration. With this, risk reduction decreased as exposure duration increased, according to the study.

"N99 masks, which are even more efficient at filtering airborne particles than N95 masks, are obviously one of the best options for blocking the virus, as they can reduce average risk by 94-99% for 20-minute and 30-second exposures, but they can be hard to come by, and there are ethical considerations such as leaving those available for medical professionals," said lead author Amanda Wilson in a press release.

According to the researchers, N95 masks and surgical masks, along with vacuum cleaner filters that can be inserted into filter pockets in cloth masks are the next best options. The vacuum filters reduced infection risk by 83% for a 30-second exposure and 58% for 20-minute exposure.

Out of the other nontraditional materials evaluated by the researchers, tea towels, cotton-blend fabrics, and antimicrobial pillowcases were the next best for protection, according to the press release. Scarves reduced infection risk by 44% after 30 seconds and 24% after 20 minutes, and cotton t-shirts showed similar efficacy. However, both were only slightly better than wearing no mask at all, according to the researchers.

Wilson and her research team collected data from various studies of mask efficacy and created a computer model to simulate infection risk, taking various factors into consideration.

"One big component of risk is how long you're exposed. We compared risk of infection at both 30 seconds and 20 minutes in a highly contaminated environment," Wilson said in a press release.

Other conditions that impact risk of infection are the number of people around you and their distance from you, as the size of virus-transporting droplets from sneezes, coughs, or even speech is crucial. Heavier droplets carrying the virus drop out of the air faster than smaller, lighter particles, which makes distance important in reducing exposure, according to the press release.

In addition, the study showed that the more time a person spends in an environment in which the virus is present, the less effective a mask becomes.

"That doesn't mean take your mask off after 20 minutes, but it does mean that a mask can't reduce your risk to zero." Wilson said in the press release. "Don't go to a bar for 4 hours and think you're risk free because you're wearing a mask. Stay home as much as possible, wash your hands often, wear a mask when you're out, and don't touch your face."

Two of the ways that masks can filter larger aerosols are through mechanical interception and inertial impaction, according to Wilson.

"The denser the fibers of a material, the better it is at filtering. That's why higher thread counts lead to higher efficacy. There's just more to block the virus," Wilson said in a press release. "But some masks, such as those made from silk, also have electrostatic properties, which can attract smaller particles and keep them from passing through the mask as well."

The researchers’ model included parameters such as inhalation rate, or the volume of air inhaled over time, and virus concentration in the air.

"For example, if we know people's inhalation rates vary by this much and know this much virus is in the air and these materials offer this much efficiency in terms of filtration, what does that mean for infection risk? We provide a range, in part, because everyone is different, such as in how much air we breathe over time," Wilson said in a press release.

The researchers emphasized the importance of having a mask that has a good seal that pinches at the nose, and that people should not wear a mask beneath the nose or tuck it under the chin when not in use.

REFERENCES

The best (and the worst) materials for masks. The University of Arizona. https://news.arizona.edu/story/best-and-worst-materials-masks. Published July 6, 2020. Accessed July 10, 2020.