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Researchers find effectiveness of homemade masks depends on fabric

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Posted at 1:26 PM, Apr 03, 2020
and last updated 2020-04-03 19:04:25-04

WINSTON-SALEM, N.C. - With masks in short supply right now, many people are making homemade masks to donate to hospitals and wear themselves.

Not all homemade masks offer the same protection, though.

Researchers at Wake Forest Baptist Health found the type of fabric used is key to their effectiveness.

A team of doctors and scientists evaluated 13 different designs from about 400 masks made by volunteers.

They wanted to see which ones did the best job at removing particles that were 0.3 - 1.0 microns in diameter. That's the size of many viruses and bacteria.

The effectiveness of the masks they tested varied widely.

According to Dr. Scott Segal, Chair of Anesthesiology at Wake Forest Baptist Health, the best homemade masks were made of two layers of high-quality, heavyweight fabric with a high thread count.

A double-layer mask with a simple cotton outer layer and an inner layer of flannel also performed well.

Some were able to achieve 79% filtration. While it's not as good as N95 masks which filtered 97% in their tests, it's actually better than surgical masks that filtered 62 - 65%.

Dr. Segal says the results surprised him.

"I was a little pessimistic that we were going to find one that worked well, but I was delighted that there is something that can make a very effective mask. And sort of our reason for doing this and for getting the word out is so that if people do choose to make masks for their own use or to donate to health care facilities, at least they try to concentrate on the most effective designs," said Dr. Segal.

Those that didn't perform as well were made of lower quality, lightweight cotton and only filtered 20%. One design only filtered 1%.

"To our surprise, adding a little insert where you could put additional materials between the layers didn't seem to help very much," said Dr. Segal," Sometimes they also made it much harder to breath through it, and that's something else to keep in mind when designing a mask."

As far as how it's designed to be worn, Dr. Segal says they'd recommend making masks that tie behind your head.

"We have not tested fit with these masks, however, the ear loop style masks are generally not used in sterile procedure areas like an operating room or procedure area because they don’t as readily conform to the shape of the face, so we prefer a tie on design if it’s going to be used in a medical setting," said Dr. Segal.

Dr. Segal also says it's important to remember - no mask is as good as social distancing and hand washing.

Related: Masks Now coalition making homemade masks, asking for volunteers

“If you must venture out, it seems like the public health recommendation may be to go ahead and wear a mask but we should be clear – you’re trying to achieve a different purpose there. The purpose of a mask for a health care worker is to protect the wearer. The purpose of a mask for the public is really a public health initiative to try to prevent asymptomatic but infected people from hurting others, not as much to protect the wearer,” said Dr. Segal.

Dr. Segal says their next step is to see how well the masks hold up to repeated washings and to try other materials, such as vacuum cleaner bags and air conditioning filters.

"It's been heartwarming to see how hard people are trying to help," said Dr. Segal, "so we’ll keep trying out different designs and testing longevity in the coming weeks."

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