Researchers say some fabrics can filter nearly as well as an N95

A new study from researchers at the University of Chicago says that a combination of cotton with silk, chiffon, or flannel can create a well-functioning filter.

However, the researchers and other experts say there’s a big caveat: If your mask leaks around the edges, unlike the tightly fitted N95, your homemade filter will lose its effectiveness.

Tighter-woven cotton alone was found to be effective, particularly two layers of 600 thread-per-inch cotton. So was a cotton quilt made of two 120 thread-per-inch cotton sheets, with a 0.5-centimeter batting of cotton, polyester and other fibers. Four layers of silk — imagine someone bundled up in a scarf — also performed well.

But the best overall filtration was provided by a sandwich consisting of one layer of the tighter-woven cotton plus two layers of silk, or two layers of chiffon, or one layer of flannel — because of the electrostatic filter created by the non-cotton layers.

“We speculate that the enhanced performance of the hybrids is likely due to the combined effect of mechanical and electrostatic-based filtration,” the study said. “Combining layers to form hybrid masks ... may be an effective approach."

In our case we always use 2 layers of tight-oven cotton, from brand new material. ( Do you want to put on your face somebody's used sheets?). And in the middle we use 1 or 3 layers of non-woven polypropylene. 

We have built an extensive source of scientific data on our website which points out the benefits and advantages of using non-woven filtration as we believe it is better than woven materials for filtration.

The problem is around the edges.

“The bad thing about using masks that have really high filtration is that, if there are any gaps in the mask, the air is just going to go through those gaps than through the filter,” Crittenden said in a telephone interview with the Globe. "It’s important to have a mask that has high breathability and high airflow, and that’s not typical of cloth masks.”

This is why we came up with a more anatomically fit face mask with elastics which fits closer to the face and has fewer gaps. 

We continue to wait for the testing results from the lab we have contracted to rate the bacterial filtration efficiency and viral filtration efficiency for our 5-layer masks. We will publish more information as soon as we receive the test results.

Source: https://www.bostonglobe.com/2020/04/30/metro/making-your-own-mask-researchers-say-some-fabrics-can-filter-nearly-well-an-n95/