The following samples were used in the study: N95 respirator and KN95 respirator; surgical mask, wash/dry coupon, 2-ply bandana, cloth mask, and surgical mask. Marina Vance
People's reusable cloth masks that they have used for years may be a little less comfortable than the ones they were wearing for the last year. New research by the University of Colorado Boulder shows that they can filter out viruses even if dried and washed.
Marina Vance (assistant professor in the Paul M. Rady Faculty of Mechanical Engineering) said that "it's good news to sustainability." You know that cotton mask you've been using to wash, dry and reuse? It is probably still good. Don't throw it out.
This study was published in Aerosol and Air Quality Research. It also confirms previous research showing that a cotton mask worn over a surgical mask provides more protection than cloth alone.
Science and sustainability
An estimated 7.200 tons of medical debris has been produced every day since the outbreak of the pandemic. Much of it is disposable masks.
Vance is also a member of the faculty for the environmental engineering program.
Vance was keen to work with scientists from the National Renewable Energy Laboratory (NREL), when they approached her about how drying and washing reusable cloth masks.
The process was simple: make double-layered cotton squares, dry them, and then wash them again (up to 52 times), and test them every 7 days.
The masks were not tested using real people, but were attached to one end of a stainless steel funnel, through which researchers could control the flow of airborne particles and air. Researchers also used realistic to real-life conditions with high humidity and temperatures to simulate the effects of our breathing on the masks.
The researchers discovered that the fabric's filtration efficiency was not affected by repeated washing and drying. However, cotton fibers did begin to fall apart after repeated washing and drying.
There was a slight increase in the mask's resistance to inhalation, which means that it may be a little more difficult for some people to breathe through the mask after some use.
It is crucial to have a good mask fit
One caveat is that the testing was done in a lab with a "perfect fit".
Vance stated, "We assume there are no gaps between mask material and person's faces."
Each person's face is different. It will fit snugly or loosely depending on the mask's shape and how well it is adjusted by the individual. Research has shown that poorly fitting masks can allow up to 50% of the airborne particles and viruses we inhale slip through.
What mask should you choose?
This is not the first study to show that cloth masks offer less protection than surgical masks, or a combination of both surgical and cloth masks.
The mask's ability to filter the air inhaled by the wearer of it. Bandanas only filtered 9% of the virus particles.
Comparatively, surgical masks removed between 42-88% and 48% of the small particles. Cotton masks placed on top of surgical masks achieved close to 40% filtration efficiency. The best masks, N95 and KN95, filtered out between 83-99% of these particles.
Vance said that although cloth masks provide less protection against the virus than disposable masks or layered approaches, this information is still important for cloth-wearers who depend on it for its affordability, comfort, and reusability.
Vance stated, "I believe the best mask is the one you actually wear." Vance said, "And that will fit snugly against your skin without being too uncomfortable."
Further exploration of Sneeze cam reveals the best fabric combinations for cloth masks
Further information: Sumit Sankhyan and colleagues, Filtration performance of layering masks and face coverings and the reusability of cotton masks after repeated washing and drying, Aerosol Research (2021). Sumit Sankhyan and colleagues, Filtration performance of layering masks and face coverings and the reusability of cotton masks after repeated washing and drying, (2021). DOI: 10.4209/aaqr.210117
