For the next several months at least, it appears the requirement to wear masks or face coverings in public places is here to stay. Scientists from two universities recently compared different types of masks, in an effort to learn which are most effective at preventing coronavirus transmission.
The two research groups, from Florida Atlantic University and the University of Arizona, evaluated commercially manufactured masks against homemade coverings made from cotton, silk and other fabrics.
The Florida Atlantic group focused its research on how well different mask materials block the travel of respiratory droplets. It found that commercially produced cone-type masks reduced the average forward distance of respiratory droplets produced by coughing, sneezing or speaking very effectively, to 8 inches. The most effective homemade masks they tested were made from stitched layers of cotton quilting; these reduced the forward travel of droplets even more, to just 2.5 inches.
Simple homemade masks such as those made from T-shirts, folded handkerchiefs and bandanas, somewhat reduced the forward projection of droplets to between 1 and 3 feet. However, they also showed significant leakage through the top and sides.
The University of Arizona team’s research centered on how well different types of masks could protect wearers from coronavirus after a short 30-second exposure to a highly contaminated area, as well as after 20 minutes. Most protective were N99 and N95 masks – with a “protection factor” of 94-99% – followed by surgical masks and, somewhat surprisingly, vacuum cleaner filters inserted into pockets in cloth masks. These reduced infection risk by 83% after 30 seconds, and 58% after 20 minutes.
Of the other materials they evaluated, tea towels, cotton-blend fabrics and antimicrobial pillowcases were the next best in terms of homemade mask protection.
“The denser the fibers of a material, the better it is at filtering,” said lead author Amanda Wilson. “That’s why higher thread counts lead to higher efficacy…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.”
Both groups found that wearing any type of mask is far more protective than none at all. Without face masks, respiratory droplets were projected as far forward as 12 feet – with an average distance of 8 feet – and stayed airborne for up to three minutes. They also found wearing a mask reduced infection risk between 24-94% after 30 seconds of exposure to droplets or by 44-99% after 20 minutes, depending on the type of mask worn. In general, the masks’ protective effects decreased as exposure time increased.