HEALTH

Not all cloth masks are created equally. How good are the free ones from Tennessee?

Vincent Gabrielle
Knoxville News Sentinel

Tennesseans are being asked to wear a face mask in public to help slow the spread of the coronavirus. The state is even handing out free ones to get everyone on board. 

Not all masks are created equally, but all of them do serve a purpose — catching potentially virus-laden droplets.

Not everyone is pleased about the loosely woven single layer of fabric used in Tennessee's free masks, which were manufactured by North Carolina-based sock company Renfro Corporation. 

Masks with dense material or layers of material are recommended, but there's no standard for how many droplets a mask must block to be considered fully effective against the spread of coronavirus. 

"I would hesitate to say that the masks being provided by the state are quote unquote 'useless,'" said Dr. David Aronoff, Division of Infectious Diseases director at Vanderbilt University Medical Center. He stressed that mask wearing is not just about personal protection. Mask wearing is a social act that promotes the public good.

"First, it helps remove stigma around wearing masks. If everyone is wearing a mask, nobody feels like they're strange." Aronoff said. "Second, it provides an important visual reminder that we need to be keeping distance from each other because we're living in a pandemic." 

While the masks being distributed by Tennessee are unlikely to totally prevent the spread of aerosols or droplets, Dr. Henry Spratt, an environmental microbiologist at the University of Tennessee Chattanooga, said they could be used to improve the fit of a bandanna-based mask. 

Scientists have found that layering thicker cotton T-shirt material, quilting cotton or other thick-but-breathable material works better than using knit cloth or wicking materials like linen or silk. Poor quality or old cotton also performs poorly

Vacuum cleaner bags may also work, but not all vacuum cleaner bags are made of nontoxic material. If you're going to use them, check the label and keep them between other layers of cloth. 

Cloth mask manufactured by Renfro distributed free at the Knox County Health Department.

Fit is also very important. If a mask does not fit properly, air will go around the mask, not through the mask. One study found that tightening mask fit using an outer layer of nylon stockings helped enhance the filtration power of cloth masks. 

"From our results, what adding the nylon layer tells you is that fit is really important, regardless of material," explained Dr. Amy Mueller, an assistant professor of engineering at Northeastern University who is studying cloth masks. "In general we found that multi-layered masks were much more effective."

The science behind whether masks prevent the spread of COVID-19 is stillunclear. The Centers for Disease Control and Prevention recommends the public wear cloth masks to help prevent asymptomatic transmission in areas where social distancing might not be possible, like a grocery store aisle. This also reduces stress on the medical supply chain. It’s a precautionary measure.

The trouble is that this is a new guideline. Standards for how effectively cloth masks catch droplets from the wearer's mouth have not been developed. 

"I think that we as a society haven't really hammered down exactly what the number (of particles filtered out) that we are trying to achieve," Mueller said. 

While a thinner, loosely woven mask material will probably catch fewer droplets both from the wearer and the surrounding environment, it could still help. Wearing any mask might be more helpful than wearing no mask at all.

How effective are cloth masks?

There hasn't been much research yet on homemade masks, but it's clear their effectiveness all depends on the material.

  • Tightly woven, thick material, like thick T-shirt cotton or quilting cotton, or sweatshirt material are good bases for a cloth mask.  
  • Thin, airy or wicking material like linen or muslin or silk is less effective than thicker material.
  • Two or three layers of material is better than one layer of material.
  • The mask has to be breathable. Don't use materials like Gore-Tex, which is too tightly woven for safe breathing.

"The question is, how porous can this be before it stops working," said Aronoff. "We don't really know the answer to that but it makes intuitive sense that a looser network of fibers has less ability to interrupt the dispersal of respiratory droplets."

Other factors that make a mask more effective:

  • If the mask does not fit, it will not work. It needs to be tight to the face and cover your nose and mouth. Using nylon stockings as an outer layer can help increase mask fit without reducing breathability.
  • Keep the mask clean. Dirty masks aren't as good at trapping particles. 

The masks distributed by Tennessee are woven from a terry polyester material and treated with a silver-based antibacterial compound, which would probably help with smell but not kill a virus. 

"That picture is amazing. I've never seen a mask like this that you could see through" Spratt said . "Only the biggest droplets would be contained."