Cotton fabrics become better filters when exposed to humid conditions. Synthetic fabrics do not.

View as a Web Page Study Indicates That Humidity in Breath Makes Cotton Masks More Effective at Slowing the Spread of COVID-19 Researchers have come up with a better way to test which fabrics work best for masks that are meant to slow the spread of COVID-19. By testing those fabrics under conditions that mimic the humidity of a person's breath, the researchers have obtained measurements that more accurately reflect how the fabrics perform when worn by a living, breathing person. The new measurements show that under humid conditions, the filtration efficiency — a measure of how well a material captures particles — increased by an average of 33% in cotton fabrics. Synthetic fabrics performed poorly relative to cotton, and their performance did not improve with humidity. The material from medical-procedure masks also did not improve with humidity, though it performed in roughly the same range as cottons. Read More PHOTO ESSAY Masks Under the Microscope See more images of what's happening on a microscopic level inside your mask. See More

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