Researchers create test to find out which masks are the least effective

A little over half a year into the COVID-19 outbreak, we have begun seeing signs of life returning to the pre-pandemic "normal." Schools are reopening, tourists are flocking back to amusement parks, and those missing their social lives are dropping into restaurants for long-awaited catch-ups. However, as much as we'd like to forget the past seven to eight months as a bad dream and pretend as though everything is fine, the novel Coronavirus continues to wreak havoc in our midst. This is why a group of researchers at Duke University came up with a simple test to determine the effectiveness of protective face masks — the most popular (unpopular in some circles) accessory of the new decade.

According to CNN, the quest for such a test began when a professor at Duke's School of Medicine—who was assisting a local group buy masks in bulk to distribute to community members in need—realized that they needed the means to make sure that the masks they bought would actually serve their purpose. Researchers with Duke's physics department then came up with a simple method that makes use of a laser beam and cell phone to evaluate the efficiency of masks by studying the transmission of respiratory droplets during regular speech.

"We use a black box, a laser, and a camera," explained Martin Fischer, one of the authors of the study published on Friday. "The laser beam is expanded vertically to form a thin sheet of light, which we shine through slits on the left and right of the box." When a speaker talks into a hole in the front of the box, a cell phone camera placed on the back of the box records the light that is scattered in all directions by the respiratory droplets cutting through the laser beam. A simple computer algorithm then counts the droplets seen in the video.

Through their study, researchers discovered that some masks utterly fail to serve their purpose. 14 commonly available masks, including a professionally fitted N95 mask, were tested 10 times each and compared against the results of a person talking without wearing a mask. Unsurprisingly, the fitted N95 — usually reserved for health care workers — was found to be most effective while three-layer surgical masks and cotton masks also performed well. On the other hand, neck fleeces, aka gaiter masks, were the least effective.

In fact, wearing a neck fleece —which is often used by runners — was found to do more harm than good as it resulted in a higher number of respiratory droplets. The material seemed to break down larger droplets into smaller particles that are easily carried away with air. Folded bandanas and knitted masks also produced similar results. "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," said Fischer said.

"We want to emphasize that we really encourage people to wear masks, but we want them to wear masks that actually work," he added. Although the setup of the test is quite simple, Fischer does not recommend that people try it at home since mishandling powerful lasers can cause permanent eye damage. However, researchers hope companies, museums, and community outreach centers will set up the test to show the general public which masks are the most effective. "This is a very powerful visual tool to raise awareness that very simple masks, like these homemade cotton masks, do really well to stop the majority of these respiratory droplets," said Fischer. "Companies and manufacturers can set this up and test their mask designs before producing them, which would also be very useful."