Humidity in breath makes cotton masks more effective at slowing the spread of COVID-19

https://www.eurekalert.org/pub_releases/2021-03/nios-hib030921.php

 

News Release 9-Mar-2021
Cotton fabrics become better filters when exposed to humid conditions; synthetic fabrics do not
National Institute of Standards and Technology (NIST)

 

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.

This study, conducted by scientists at the National Institute of Standards and Technology (NIST) and the Smithsonian's Museum Conservation Institute, was published in ACS Applied Nano Materials.

An earlier study by the same research team showed that dual-layer masks made of tightly woven cotton fabrics with a raised nap, such as flannels, are particularly effective at filtering breath. That study was conducted under relatively dry conditions in the lab, and its main finding still stands.

"Cotton fabrics are still a great choice," said NIST research scientist Christopher Zangmeister. "But this new study shows that cotton fabrics actually perform better in masks than we thought."

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