@diymom noted that the bioskin (I think) company tested the filtering of their masks. The NYTimes has an article about the filtering abilities of various combinations of mask layers and filters:
https://www.nytimes.com/2020/11/24/...=footer&req_id=731223666&surface=most-popular
From the article:
"
Three layers are better than two. The best mask has two tightly woven layers of outer material with a filter material sandwiched in the middle, Dr. Marr said. You can use surgical mask material or even a piece of a vacuum bag as a filter between two pieces of fabric. Coffee filters are an option, but can be less breathable. If you like your two-layer mask, you can just wear it over a surgical mask when you want added protection. A well-fitting fabric mask with a third filter layer can stop 74 to 90 percent of risky particles, the researchers found.
Flexible material is better. Stiff material creates gaps. Look for a mask made of tightly woven flexible material that contours to your face. Masks with wire that can be molded around the nose also fit better by closing gaps where air can escape out and seep in.
Ties are better than ear loops. Masks that tie around your head fit better and can be more comfortable. Ear loop masks can leave bigger gaps around your face and cause ears to become sore with longer use.
Face shields should be used with a mask. Face shields alone offered little to no protection. Although the clear plastic shield is impermeable, air seeps out and comes in around the edges of the shield. “It was the worst of everything,” said Jin Pan, a civil and environmental engineering Ph.D. student who was a co-author of the study. A face shield combined with a mask offers added protection, particularly for the eyes.
A well-fitted mask protects the wearer. Dr. Marr and her colleagues tested cloth masks for how well they protected others (outward protection) as well as the wearer (inward protection). Although masks are most efficient at filtering outgoing germs, they do stop incoming germs at nearly the same rate in most cases, the researchers found. Masks that did a poor job protecting the wearer were those made of stiffer materials and those worn loosely and with gaps around the edges.
A recent study from Denmark suggested that masks don’t protect the wearer, but Dr. Marr noted that in that study, many people weren’t using masks properly. “Fewer than half wore them as instructed,” Dr. Marr said. Although Dr. Marr’s findings come from a lab, rather than the real world, she said her group’s latest research should offer reassurance to people who wear well-fitted masks that they are getting additional protection from other people’s germs.
The research should also reassure people about the benefits of cloth masks, Dr. Marr said. She noted that masks can’t do “100 percent of the work,” and it’s important to combine mask wearing with other measures, like hand-washing and restricting social contacts. "