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Adding a Nylon Stocking Layer Could Boost Protection From Cloth Masks: Study

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Researchers at Northeastern University have found that adding an outer layer made from nylon stockings to a homemade face covering can boost its ability to filter out small particles in the air by creating a tighter seal between the mask and the wearer's face. In some cases, that extra nylon layer helped homemade cloth masks match or exceed the filtering capability of medical-grade surgical masks.

"It really improved the performance of all of the masks, and it brought several of them up and over the baseline mask we were using, which was a 3M surgical type mask," says Loretta Fernandez, an assistant professor of civil and environmental engineering at Northeastern University, one of the scientists who conducted the research.

Researcher Loretta Fernandez of Northeastern University wears a homemade face mask without and with an extra outer layer made from nylon stockings (right). The added nylon outer layer significantly boosted masks' ability to filter out small particles, her research found.

Even the surgical mask performed better in their study: Testing showed it went from blocking out 75% of small particles to 90% with the addition of a pantyhose overlayer. An N95 respirator, by comparison, is designed to block out at least 95 percent of small particles when worn properly.

"Adding a layer that keeps the mask tight to the face is going to improve the function of any of these masks," Fernandez explains, "because how well they protect us is not only a matter of what material we're using to do the filtering but also how well [the mask] seals to the face, so that we're trying to avoid air making it around the mask into our breathing zone." The pantyhose layer, she says, helps creates a tighter seal around the face to reduce how much air leaks around loose edges — similar to the seal on an N95 respirator.

The research has not yet been peer-reviewed, but it was posted Wednesday on the scientific preprint site medRxiv and on the university's website in the interest of sharing information quickly. Scientists who reviewed the study at NPR's request praised it as vitally needed work.

Read the full story on NPR's Goats and Soda blog.

--Julia Scott (@juliascribe)

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