The controversy stemmed from one part of the peer-reviewed study in which the researchers, described by Warren as laser experts, tested a common type of neck gaiter made of a thin polyester spandex material using the contraption they created. They observed that the single-layer gaiter appeared to perform slightly worse than their no-mask control group, leading the researchers to suggest that the porous fabric may be producing smaller respiratory droplets that can hang around in the air longer. The result of the gaiter test was highlighted by the scientists in interviews as well as in a video about the study produced by the university.
“It’s not the case that any mask is better than nothing,” chemist and physicist Martin Fischer, the study’s lead researcher, said in the video. “There are some masks that actually hurt rather than do good.”
But amid heightened concerns about the efficacy of gaiters, other experts are now pushing back against the characterization that such face coverings may be “worse than nothing,” as one of the Duke study’s authors told CBS News.
In response to the Duke study, aerosol scientists have conducted their own gaiter experiments, studying the face covering’s ability to block droplets and whether it is possible to produce smaller particles similar to what the Duke researchers saw. The new research showed that when a single-layer gaiter is worn doubled up, it is highly effective at blocking a range of particle sizes, according to the results of tests done by Linsey Marr, a civil and environmental engineering professor at Virginia Tech who studies aerosols. (In the Duke study, the gaiter tested was not folded over.) Marr’s work has been supplemented by research from Ryan Davis of Trinity University in Texas, who shot water droplets at a strip of woven polyester spandex material taken from a gaiter and did not see any particle breakup or transmission. Meanwhile, Christopher Cappa, a professor at the University of California at Davis, suggested that the high number of particles detected during the Duke gaiter test may be partly due to fibers shedding from the fabric.
The results of the separate experiments were shared by the scientists on Twitter and not peer-reviewed, but Marr said the findings support the argument that even thin gaiters are “better than nothing.”
“Gaiters are as effective as a mask made out of a similar material,” Marr said. “If you double over a neck gaiter, you can get very good protection.”
Marr tested two neck gaiters using a method that is similar to a procedure developed by the National Institute for Occupational Safety and Health to certify N95 masks. One of the gaiters was thin and 100 percent polyester, while the second was a thicker, double-layer microfiber covering made of polyester and elastane, a material commonly known as Lycra or spandex.
Each gaiter was placed on a mannequin head inside a chamber with purified air, and a liquid salt solution and medical nebulizer was used to simulate saliva. The nebulizer generated a fine mist that was shot through the mouth of the mannequin at a speed that mimics talking. The droplets were aimed at another mannequin head a foot away and “gold-standard equipment,” usually reserved for aerosol science labs, tracked the particles, Marr said.
Neither gaiter performed well when very small particles measuring 0.5 microns were sprayed, blocking only about 20 percent of the droplets of that size, Marr’s research found. (Hospital-grade N95 masks are typically tested using particles that are 0.3 microns.)
But at one micron, the particle size that experts say is relevant to transmission, Marr observed that the two gaiters were both able to stop at least 50 percent of the droplets.
“Once you get up to three microns, they block over 90 percent,” she said, adding that there were no statistically significant differences between the gaiters tested and a cotton cloth mask that meets the requirements for the non-sewn mask design promoted by the Centers for Disease Control and Prevention.
The thin gaiter’s effectiveness increased when Marr folded it over to create two layers. For all the particle sizes tested, the doubled-up gaiter was more than 90 percent effective, according to the research.
Marr said she “absolutely” would wear a neck gaiter herself as long as it is doubled over.
“I had my kids wearing them early on,” she said.
Based on her findings, Marr concluded that gaiters, even single-layer ones, are “better than nothing” and cast doubt on the Duke researchers’ theory that the breathable fabric was somehow responsible for creating the smaller droplets their device detected.
“Filtration doesn’t work like a sieve,” Marr said.
Over in San Antonio, Davis, an assistant professor of chemistry, conducted his own test, shooting 100-micron water droplets at a strip of material taken from a Buff-brand gaiter. He saw no evidence of the droplets breaking up upon impact.
“We actually observed the opposite; hundreds of thousands of droplets accumulated on top of the mask material and coalesced into a single, larger drop,” Davis said in an emailed statement. “This really suggests the neck gaiter material is efficient at filtering the majority of large droplets generated during speaking and is still much better than no mask at all.”
One possible explanation for the higher particle count recorded during the gaiter test performed at Duke is that the fabric itself was shedding fibers, said Cappa, who has been studying mask efficacy and aerosol particle emission.
Using a thin gaiter made out of 100 percent polyester microfiber, Cappa ran tests in which he wore the covering while performing various actions such as speaking aloud, mouthing words silently and moving his jaw around in a motion similar to chewing.
The tests showed more particles being emitted when Cappa was wearing the gaiter compared with trials of the different scenarios done barefaced.
Cappa said he and his team believe that the friction between people’s faces and masks while they are speaking or moving their mouths may cause some of the fibers in the fabric to break down. In a lab setting, the airflow ends up carrying the particles to the detector.
“So what we’re actually looking at is a combination of the particles that we are actually expiring or exhaling and the particles that are getting produced from friction with the mask, from fibers on the mask or even skin cells as well,” he said.
The issue is that the researchers have been unable to distinguish the particles based on their origins, Cappa said. But, he noted, mask effectiveness can probably be inferred when the findings are combined with results from other experiments, such as the tests conducted by Marr.
“It allows us to say that even if the gaiters are shedding these fibers, that they’re doing as good a job as many other cloth masks on reducing excretory particle emissions,” he said.
Though Warren stressed that the Duke study — a proof-of-concept paper presenting the simple testing device — never intended to “decimate an industry based on one person and one gaiter,” he said he and the other authors “happily stand behind our experimental data.”
“The measurements are what they are,” Warren said, adding that the Duke team is “delighted” to see the emergence of new research.
In response to Cappa’s alternative explanation of fiber shedding, Warren said the suggestion is “certainly not a crazy idea.” But it’s not necessarily a reassuring one, he said. “It still scares me as an explanation, because it means that stuff is getting through there that wouldn’t get through for other masks.”
For instance, Cappa noted that there is the possibility that if some of the fibers coming off the masks are contaminated, then it could be a potential source of infectious particles. It is critical that people regularly wash their cloth masks, he said.
The continued debate over the effectiveness of gaiters highlights the challenges faced by researchers who are aiming to provide answers to the public amid a pandemic plagued by widespread uncertainties. Testing non-medical-grade coverings has been especially difficult, said Christopher Sulmonte, project manager for the Biocontainment Unit at Johns Hopkins Medicine.
“We’re looking at types, we’re looking at materials, but it’s also how those materials are formed into the mask or how many layers the mask has,” Sulmonte said. “There’s a lot of variables that have to be considered.”
When choosing a mask, Sulmonte urged people to prioritize fit, function and frequency: whether the mask fits properly with little to no gaps, whether the material is opaque and layered, and whether it can be worn consistently.
Sulmonte said he wears a two-layer cotton mask with a filter and ear loops, and he would recommend similar masks over a neck gaiter. By design, gaiters are harder to remove safely, because pulling them down involves touching the fabric, which may be contaminated, he said, adding: “So, from an infection-control standpoint, that could be a little less effective.”
“The big thing is that we know that there are masks that work better,” he said.