Health and Wellness

Study: The most and least effective face masks to use during the pandemic

LeoPatrizi | E+ | Getty Images

A recent study out of Duke University suggests that not all face coverings are equally effective at preventing the spread of Covid-19. 

While wearing a face mask or cloth covering when you're outside the home is one of the best things you can do to stay safe, not all masks are as good at filtering out potentially harmful particles like coronavirus.

In experiments, bandanas, handkerchiefs, fleece balaclavas (cold-weather gear that covers the entire face except for the eyes) and neck gaiters (tubes of performance fabric typically used for running outdoors), offered very little protection, while N95 respirators, surgical masks and even homemade cloth masks performed better.

For the experiments, researchers in the Duke Department of Physics positioned a laser beam in a dark box that would illuminate respiratory droplets as they pass through the light. A speaker then positioned their mouth by a hole to the box and said a phrase while a camera (in this case, an iPhone camera) on the other end of the box captured video of the droplets in real time.

The researchers tested a total of 14 common face coverings, then analyzed the video frame by frame using a computer algorithm that counts the number of particles visible. Participants said the phrase "Stay healthy, people" five times into the laser, a total of 10 times for each mask.  

The neck gaiter (No. 11 in the photo below), which was made of polyester spandex material, performed the worst in the study, actually producing more particles than speaking with no face covering at all.

"We attribute this to ... the textile breaking up those big particles into many little particles," Dr. Martin Fischer, chemist, physicist and study author, said in a video release. "They tend to hang around longer in the air, they can get carried away easier in the air, so this might actually be counterproductive to wear such a mask."

A bandana tied to cover the nose and mouth only offered slightly more protection than no mask at filtering particles. 

Researchers tested 14 different common face masks and cloth coverings, from bandanas to neck gaiters and even N95 respirators.
Photo Credit: Emma Fischer, Duke University.

The N95 respirator with no valve (No. 14 in the photo) was the most effective in the study, but experts say that these devices are in short supply should be reserved for healthcare workers.

A disposable surgical mask made from a plastic-derived material called polypropylene (No. 1 in the photo) was the next best option, followed by a mask made from two layers of cotton and one layer of synthetic material (No. 5 in the photo). Another recent study that utilized similar technology suggests that cloth face masks need at least two to three layers of fabric in order to be protective, and the CDC recommends using two layers of quilting fabric or cotton sheets for homemade masks.

Masks made from cotton fabric alone (numbers 6, 7, 8, 9, 10 and 13), as well as knit t-shirts (No. 3 in the photo) performed about the same. Though other evidence suggests that wearing a cloth may provide protection for the wearer, not just those in close proximity.

Interestingly, N95 respirators with exhalation valves did not rank well — and the CDC doesn't recommend wearing these masks. (While masks with valves work well at protecting you from the air around you, the exhalation valve may allow unfiltered exhaled air to escape and harm others, according to the CDC.)

So what does this mean? All things considered, the best option for the average person is to wear either a surgical mask or a homemade cotton mask with multiple layers.

"We want to emphasize that we really encourage people to wear masks, but we want them to wear masks that actually work," Fischer told CNN Saturday.

More research needs to be done that addresses variations in masks, speakers and how people wear them, Fischer said.

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