The Science Behind The Best Homemade Masks

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The Science Behind The Best Homemade Masks
Scarves, bandanas, T-shirts and towels are among the things researchers studied for effectiveness against viruses.
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Many of us are venturing out with faces covered by cloth from whatever we can dig out of our closets to ward off coronavirus.

The CDC recommendations for do-it-yourself masks say use "tightly woven cotton," but researchers are getting an idea about which household fabrics actually work best.

“We’ve tried everything from coffee filters to vacuum bags, pillowcases, sheets, different scarf materials,” said Joel Burken, part of a team led by Yang Wang at the Missouri University of Science and Technology.

The researchers found cloth masks actually allow most virus sized particles to pass through.

 — Two layers of a cotton bandana block just 18% of particles

 — Two layers of a wool scarf are a little better, filtering out 21%

 — A 600 thread count pillowcase was 22% effective

 — The more of any fabric you layer the better, as long as you can breathe. Four layers of 600-thread count pillowcase fabric are 58 percent effective

The Missouri team found the best face covering, performing even better than a surgical mask, may be a piece of air filter for something like a furnace or air conditioning, sandwiched in cloth to prevent inhaling fibers from the filter itself.

After the swine flu outbreak, scientists in 2010 conducted a similar study of homemade masks for the CDC’s National Institute for Occupational Safety and Health.

Results showed sweatshirts and towels did the best job defending against nano-sized particles like a virus. 

“The best materials were the fuzzy fabrics, anything that had a very high amount of surface area,” said Ben Eimer, who worked on the CDC NIOSH experiment.

What didn’t do so well?

Tee shirts, blocking just 13 percent of particles, and handkerchiefs, only 11 percent effective.

“Like the old-style, your grandfather carried it in his pocket, handkerchiefs,” Eimer said. “They were the worst.”

Homemade face coverings can’t compete with N95 masks in short supply, shown to be more than 99 percent effective against viruses.

But researchers found homemade face covering of any variety have a major benefit: they are a reminder not to touch the face to reduce one major source of virus transmission.