Face masks are “the most powerful weapon we have” against the coronavirus, CDC director Robert Redfield said last month, but some face coverings may be more effective than others.
With most Americans now required to wear masks in public spaces, researchers have tested the different types of masks — from the N95 masks most commonly worn by healthcare workers to cloth masks and bandanas — to determine which kind best reduces the spread of respiratory droplets.
Last week, a study published in Science Advances found that the N95 masks were most effective, while disposable surgical masks and homemade cotton masks were also found to limit the transmission of droplets.
The study gained widespread attention after news reports said the findings showed that neck gaiters, which have become common among runners and other athletes for their breathability, may be less effective than not wearing a mask at all. The researchers, from Duke University, found that the material in neck gaiters split larger respiratory droplets into smaller ones that were then expelled through the fabric, potentially spreading germs further than if a person was not wearing any mask at all.
But the researchers later clarified that their findings were misrepresented.
“Our intent was not to say this mask doesn’t work, or never use neck gaiters,” said Martin Fischer, an associate research professor in the department of chemistry at Duke and a co-author of the study told The New York Times. “This was not the main part of the paper.”
Getty Mom and daughter wearing face masks
To dig deeper into the effectiveness of neck gaiters, Dr. Linsey Marr, a professor of civil and environmental engineering at Virginia Tech and one of the world’s leading authorities on aerosols, who did not work on the Duke study, set up her own test. Using foam model heads that sprayed out a saliva-like solution, she and Jin Pan, a Virginia Tech graduate student who studies aerosols, tested two types of neck gaiters. One was made of a single layer of 100 percent polyester, while the other was two layers of 87 percent polyester and 17 percent elastane fabric.
Both gaiters stopped 100 percent of large droplets, and 50 percent or more of small, 1-micron droplets. The double layer gaiter was more effective, but both types of gaiters were better than wearing nothing at all.
“I’ve been recommending neck gaiters, and my kids wear neck gaiters,” Marr said. “There’s nothing inherent about a neck gaiter that should make it any worse than a cloth mask. It comes down to the fabric and how well it fits.”
The Duke researchers found that cloth masks were the most effective type of non-medical mask, and prevented the spread of respiratory droplets at about the same rate as paper surgical masks. They also warned against wearing N95 masks with ventilator valves.
“Those relief valves are fantastic if what you want to do is protect yourself from the outside world because air doesn’t come in through them,” one of the study’s co-authors, Warren S. Warren told The Washington Post. “If what you’re trying to do in this pandemic is protect the outside world from you, it completely defeats the purpose.”
The Centers for Disease Control and Prevention have also recommended against wearing masks with exhalation valves.
“The purpose of masks is to keep respiratory droplets from reaching others to aid with source control,” an update on the CDC website reads. “Masks with one-way valves or vents allow exhaled air to be expelled out through holes in the material. This can allow exhaled respiratory droplets to reach others and potentially spread the COVID-19 virus.”
Though some are better than others, Warren said that most masks do really help slow the spread of coronavirus.
“You can really see the mask is doing something,” he said. “There’s a lot of controversy and people say, ‘Well, masks don’t do anything.’ Well, the answer is some don’t, but most do.”
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