Researchers created a test to determine which masks are the least effective

https://www.cnn.com/2020/08/08/us/duke-university-face-mask-test-trnd/index.html

By Alaa Elassar, CNN

Updated 9:06 PM ET, Sat August 8, 2020

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a group of researchers at Duke University created a simple technique to analyze the effectiveness of various types of masks which have become a critical component in stopping the spread of the virus.

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In the study published Friday, researchers with Duke's physics department demonstrated the use of a simple method that uses a laser beam and cell phone to evaluate the efficiency of masks by studying the transmission of respiratory droplets during regular speech.

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But when testing their effectiveness, researchers discovered that some masks are quite literally useless.
Researchers tested 14 commonly available masks including a professionally fitted N95 mask, usually reserved for health care workers. First the test was performed with a speaker talking without wearing a mask. Then they did it again while a speaker was wearing a mask. Each mask was tested 10 times.
The most effective mask was the fitted N95. Three-layer surgical masks and cotton masks, which many people have been making at home, also performed well.

Neck fleeces, also called gaiter masks and often used by runners, were the least effective. In fact, wearing a fleece mask resulted in a higher number of respiratory droplets because the material seemed to break down larger droplets into smaller particles that are more easily carried away with air.

Folded bandanas and knitted masks also performed poorly and did not offer much protection.

"We were extremely surprised to find that the number of particles measured with the fleece actually exceeded the number of particles measured without wearing any mask," Fischer said. "We want to emphasize that we really encourage people to wear masks, but we want them to wear masks that actually work."

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