New face mask study determines which types are most effective

A new study out of Duke University used a laser beam to determine which types of masks are most effective.

The researchers found one specific type of face covering, a neck gaiter, is potentially worse than not wearing a mask at all.

The team, led by Dr. Martin Fischer, compared 14 different face coverings, from surgical masks to bandanas.

They had a subject speak the same phrase — "Stay healthy, people" — while wearing each face covering, and used a laser to illuminate the droplets that made it past the mask into the air.

"It was a real eye-opener to see how many particles are actually emitted, just by speaking," Dr. Fischer said. "It doesn’t take a sneeze, it doesn’t take a cough, just simply speaking will emit plenty of particles."

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The team found a fitted N-95 mask performed best, transmitting less than 1% of respiratory droplets into the air. Dr. Fischer said a standard surgical mask was nearly as effective.

They tested a variety of cotton face coverings, from homemade pleated masks to double-layer Olson-style masks.

"They all performed on a similar level," Dr. Fischer said. "They retained about 80% of the droplets, which is a pretty good number."

This graph shows the droplet transmission from the 14 types of face coverings tested in this experiment. The green dot represents the droplet count for the control trial (a person not wearing a mask). The red dot shows bandana use, emitting about 50% of droplets, which is not very effective compared to the other masks tested.

The neck wrap, also called a neck gaiter, performed the worst in this experiment. Dr. Fischer said their results showed this type of covering may be worse than not wearing a mask at all.

"They are often a stretchy, breathable material, so not only do they not retain the droplets, but they also sort of splash them and splatter them into smaller particles," Dr. Fischer explained. "Big particles might just sink to the ground where they stay, but little particles tend to hang around longer in the air and get carried away easier in the air, so this might actually be counterproductive to wear such a mask."

Dr. Frank Rhame, an Allina Health Infectious Disease Physician at Abbott Northwestern who has treated dozens of seriously ill COVID-19 patients, said these are important findings for Minnesotans to consider.

"This is an important step in trying to understand how you should construct your mask," Dr. Rhame said.

At least 34 states, including Minnesota, now have mask mandates in place in order to stop the spread of the coronavirus.

"There are a couple of things people don’t fully recognize," Dr. Rhame said. "One is that asymptomatic people can spread this disease quite readily. And two, that the spread is mostly by the droplets that come out of our mouths while we’re talking."

Dr. Rhame said he hopes people pay attention to these types of studies, so they can select masks that offer the most protection.

"There’s a substantial decrease in the [number] of particles that you liberate into the atmosphere when you wear a mask and that helps reduce community spread, which is essential to keeping the number of people dying before we get a vaccine, low," Dr. Rhame said.

To review the full study from Duke University, click here.