Editor's note: This story, dating from April 2020, contains outdated information about masks for the COVID-19 pandemic. As of Jan. 24, 2022, according to the CDC: “Loosely woven cloth products provide the least protection, layered finely woven products offer more protection, well-fitting disposable surgical masks and KN95s offer even more protection, and well-fitting NIOSH-approved respirators (including N95s) offer the highest level of protection."
Additionally, the researchers later corrected an error in the experiment described below that had led to an overestimate in the reported efficiency of cloth masks. The revised work reconfirmed the key qualitative findings of the original paper that higher threadcount fabrics and multiple layers performed better, and that even small gaps led to poor performance.
In the wake of the COVID-19 pandemic, the U.S. Centers for Disease Control and Prevention recommends that people wear masks in public. Because N95 and surgical masks are scarce and should be reserved for health care workers, many people are making their own coverings out of fabric. Now, a preliminary study published in ACS Nano by University of Chicago and Argonne National Laboratory researchers suggests that a combination of masks made of high thread-count cotton with natural silk fabric or a chiffon weave can effectively filter out aerosol particles––if the fit is good.
“There is a huge interest and need for homemade cloth masks, but we found little data on how good various fabrics are as filters for masks,” said senior author Supratik Guha, professor with the University of Chicago’s Pritzker School of Molecular Engineering and a scientist at Argonne. “According to these results, it’s possible to get very good filtering with commonly available fabrics, but the wearer only gets maximum protection if the fit is very close to your face.”
COVID-19 is thought to spread mainly through respiratory droplets created when an infected person coughs, sneezes, speaks or breathes. Guha and his colleagues wanted to study the ability of common fabrics, alone or in combination, to filter out aerosols similar in size to respiratory droplets. So Guha—in regular times, a leading scientist in microelectronics and materials for quantum information—quickly rigged up an experimental setup with his colleagues to test combinations of fabrics that can be bought at fabric and retail stores.