Study by UChicago, Argonne researchers found fit is key to protect wearers against COVID-19
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.
The experiments took place in two plexiglass boxes connected by a tube. In one chamber, the team created a cloud of particles and blew them toward the tube, which was covered by different combinations of cloth. Mike Schmoldt and Greg Moss, environmental safety experts at Argonne who specialize in respirator testing and the effects of aerosol particles, used laboratory-grade scientific instruments to measured the number and size of particles in the chambers before and after passing through the fabric.
According to their results, one layer of a tightly woven cotton sheet, combined with two layers of polyester-based chiffon—a sheer fabric often used in evening gowns—filtered out the most aerosol particles (80% to 99%, depending on particle size). Substituting the chiffon with natural silk or a polyester-cotton flannel, or simply using a cotton quilt with cotton-polyester batting, produced similar results.