Two-Layer DIY Masks Minimize Droplet Spray From Speaking, Coughing, Sneezing

By Linda Carroll

July 29, 2020

(Reuters Health) - Do-it-yourself facemasks are far more effective at containing droplets if they are made of two or three layers of fabric compared to just one, a new study finds.

Using video and special lighting, researchers graphically showed that fewer droplets generated by speaking, coughing and sneezing escape the mask, and they don't spread as far when masks have multiple layers, according to the report published in Thorax.

"The number of layers in your mask matters," said study coauthor Raina MacIntyre, a professor and head of the biosecurity program at the Kirby Institute at UNSW Sydney, in Australia. "The more layers the better."

There is a tradeoff between protection and breathability as the number of layers increases, McIntyre allowed.

"The more layers, the less comfortable masks become," she said in an email. "However, three layers is quite comfortable."

McIntyre suspects that it's possible to create a homemade mask that is comparable to a surgical mask. But, she said, "we really cannot say that without evidence. It is possible to design a cloth mask that could be as protective as a surgical mask - but research is needed to prove that."

To take a closer look at how effectively one- and two-layer fabric masks block droplets spewed out by people talking, coughing or sneezing, McIntyre and her colleagues used a tailored LED lighting system and a high-speed camera to film the dispersal of airborne droplets produced by a healthy person with no respiratory infection.

The masks were made from a single or double layer of T-shirt fabric, which had a thread count of 170/inch. For comparison, the researchers also filmed the same experiment with a surgical mask.

Freeze frames from the video showed that while the surgical mask was most effective, the two-ply mask did a fairly good job at limiting the distance droplets traveled. Even the one-ply mask was helpful.

The type of fabric also makes a difference, MacIntyre said.

"The effectiveness of a mask depends on several factors other than filtration - which is what we tested," she added. "For example, the outer layer should be made of a water-resistant fabric such as polyester. Many people use pure cotton for the outer layer - it is fine for the inner layer but not the outer layer. It is also best to use fabrics with high thread count and fine weave."

MacIntyre also advised that people keep their masks clean. "A cloth mask must be washed every day after use," she said.

"It reaffirms that multiple layers are more effective," said Dr. Panagis Galiatsatos, an assistant professor in the division of pulmonary and critical care medicine at the Johns Hopkins School of Medicine, in Baltimore, who wasn't involved in the study.

That's helpful when counseling people in the local communities, especially disadvantaged ones, Dr. Galiatsatos said. "It reaffirms the value of a cost-effective face mask at blocking the larger aerosols that have more virus in them," he added. "It wouldn't stop the naked virus, but to cause an infection you need a high concentration of the virus."

SOURCE: Thorax, online July 24, 2020.