Virginia Tech study finds cloth masks work 'reasonably well' to prevent COVID transmission

BLACKSBURG, Va. (ABC7) — A Virginia Tech study found that cloth masks, while they're not N95 masks, they do tend to work "reasonably well" in preventing transmission of some air particles.

According to Linsey Marr, the lead researcher in the study and airborne disease transmission expert and Engineering Professor at Virginia Tech, the study started in March.

Marr says that cloth masks work "reasonably well" for aerosols 1-2 microns and larger, which she says is about the size which experts think "mostly mediates transmission."

The study evaluated the effectiveness of 11 face coverings for filtration efficiency, inward protection efficiency and outward protection efficiency, which they tested on manikins.

Some of the materials included a microfiber, coffee filter, MERV 12 filter, cotton, acrylic, bandana, CDC sewn and non-sewn designs, and a surgical mask.

The research found that the vacuum bag, microfiber cloth and surgical mask had the best material efficiency at <>>50%. Out of the materials, the thin acrylic and face shield performed the worst, the study found.

How the mask was fitted was most important in determining the efficiency of the material, the study also found.

The researchers recommended a three-layer mask with outer layers of flexible, tightly woven fabric and an inner layer of a material designed to filter out particles. According to the Virginia Tech study article, "a three-layer mask consisting of outer layers of a flexible, tightly woven fabric and an inner layer made from one of several materials designed to filter small particles, should provide at least 74 percent material filtration efficiency for the most penetrating particle size."

This combination should produce an overall efficiency of <>>70% at the most penetrating particle size and <>>90% for particles 1 [micron] and larger if the mask fits well.

The average size of respiratory droplets produced by breathing and speaking is found to be around the size of a micron, the article adds. Marr and her team found that the right materials for face coverings can have a filtration efficiency of 75 percent, with normal fabrics having about a 40 percent efficiency. In some cases, materials can have an overall efficiency of more than 90 percent.

“It’s not something I would ask a health care worker to wear in high-risk situations,” Marr said. “They need the best protection we can get. But given that it’s impractical to have everyone in the general public walking around wearing an N95, I think homemade masks are definitely helpful.”