“It’s very straightforward, doesn’t take much resources,” Fischer said in a video produced by Duke. “Any research lab has these things lying around.” Testing the face coverings was equally uncomplicated, according to the study published Friday in Science Advances, a peer-reviewed journal. Speakers said the same phrase into the box without a mask and then repeated the process while wearing one. Each face covering was tested 10 times. Inside the device, the airborne particles passed through a sheet of light created by the laser hitting the lens and produced visible flashes that were recorded by the phone’s camera. “Even very small particles can do this kind of [light] scattering,” Warren said. “We were able to use the scattering, and then tracking individual particles from frame to frame in the movie, to actually count the number of particles that got emitted.”
A fitted N95 mask, which is used most commonly by hospital workers, was the most effective, Warren said, noting that the mask allowed “no droplets at all” to come out. Meanwhile, a breathable neck gaiter, well-liked by runners for its lightweight fabric, ranked worse than the no-mask control group. The gaiter tested by the researchers was described in the study as a “neck fleece” made out of a polyester spandex material, Warren said.
“These neck gaiters are extremely common in a lot of places because they’re very convenient to wear,” he said. “But the exact reason why they’re so convenient, which is that they don’t restrict air, is the reason why they’re not doing much of a job helping people.” A number of prominent activewear companies make neck gaiters, and they are generally not designed for medical use. In April, for example, Buff, a company known for multifunctional head and neckwear, issued a public statement emphasizing that its products are not scientifically proven by the CDC and the World Health Organization to be a useful form of protection during the pandemic.
“Buff performance head and neckwear are not intended to be used as medical-grade face masks or as a replacement for N95 respirators as effective measures to prevent disease, illness, or the spread of viruses,” the statement said. Another neck gaiter manufacturer, however, cautioned against writing off every variation of the face covering based solely on the Duke study’s findings. “All gaiters are not created equal,” Chris Bernat, co-founder of South Carolina-based Vapor Apparel, said. “There’s a segment of this category that’s of a much higher quality that’s engineered to be layered.” Although the study did not provide detailed specifics about the material of the neck gaiter that was tested, Bernat raised doubts about the material’s quality. “Chances are it was a promotional quality, like a lower-quality fabric, and based on that I’m sure it didn’t perform well,” said Bernat, who has been making neck gaiters for more than a decade.
The CDC recently updated its guidelines on masks, noting that the agency does not recommend the use of coverings that have valves or vents. “This type of mask does not prevent the person wearing the mask from transmitting COVID-19 to others,” the CDC wrote. Warren encouraged people to assess their face coverings with another basic test. “If you can see through it when you put it up to a light and you can blow through it easily, it probably is not protecting anybody.” Still, he stressed that people without access to medical-grade masks shouldn’t worry.
“We’re not as a society going to be having everybody wear disposable N95 face masks,” he said. “It’s not affordable, and it’s not reasonable.” The researchers specifically made note of the effectiveness of common cotton cloth masks, finding that several of the ones tested performed about as well as surgical masks, which come in second to the N95. Experts with the WHO have recommended that fabric masks should ideally have three layers.
Although the study was “not a clinical trial” that involved testing “10,000 patients and seven different languages and all possible conditions,” Warren said its general conclusions still stand. “We’re very careful not to over-claim here,” he said. “We are not going to try to say our evidence is that this is the thread count you should use on the sheet for the two-ply cotton mask that you’re making. “But the broad take-home picture — that masks do work in cutting down transmission and that some masks that you can easily get are better than others — potentially has value in protecting everybody and getting us out of this awful situation,” he added.
Warren said he and his fellow researchers are now focused on producing a step-by-step instruction guide for creating the testing device. The team has already been approached by people from foreign countries who have expressed interest, he said.
“It is quite possible for people with a modest amount of scientific training to use this quite safely and quite effectively,” Warren said, noting that he does not recommend that the average person go out and try to construct the device themselves. “The idea is that you could have community centers, groups that are helping to test out different designs. Particularly as we’re trying to provide face masks to a large number of people who don’t have them, you want to be providing ones that work.”