The best-performing designs were a mask constructed of two layers of high-quality, heavyweight “quilter’s cotton,” a two-layer mask made with thick batik fabric, and a double-layer mask with an inner layer of flannel and outer layer of cotton.
Bonnie Browning, executive show director for the American Quilter’s Society, said that quilters prefer tightly woven cottons and batik fabrics that stand up over time. Ms. Browning said most sewing machines can handle only two layers of fabric when making a pleated mask, but someone who wanted four layers of protection could wear two masks at a time.
Ms. Browning said she recently reached out to quilters on Facebook and heard from 71 people who have made a combined total of nearly 15,000 masks. “We quilters are very much in the thick of what’s going on with this,” said Ms. Browning, who lives in Paducah, Ky. “One thing most of us have is a stash of fabric.”
People who don’t sew could try a folded origami mask, created by Jiangmei Wu, assistant professor of interior design at Indiana University. Ms. Wu, who is known for her breathtaking folded artwork, said she began designing a folded mask out of a medical and building material called Tyvek, as well as vacuum bags, after her brother in Hong Kong, where mask wearing is common, suggested it. (DuPont, the maker of Tyvek, said in a statement that Tyvek is intended for medical apparel, not masks.) The folded mask pattern is free online, as is a video demonstrating the folding process. In tests at Missouri University and University of Virginia, scientists found that vacuum bags removed between 60 percent and 87 percent of particles. But some brands of vacuum bags may contain fiberglass or are harder to breathe through than other materials, and shouldn’t be used. Ms. Wu used a bag by EnviroCare Technologies, which has said it does not use fiberglass in its paper and synthetic cloth bags.
“I wanted to create an alternative for people who don’t sew,” said Ms. Wu, who said she is talking to various groups to find other materials that will be effective in a folded mask. “Given the shortage of all kinds of materials, even vacuum bags might run out.”
The scientists who conducted the tests used a standard of 0.3 microns because that is the measure used by the National Institute for Occupational Safety and Health for medical masks.
Linsey Marr, a Virginia Tech aerosol scientist and an expert in the transmission of viruses, said the certification method for respirators and HEPA filters focuses on 0.3 microns because particles around that size are the hardest to catch. While it seems counterintuitive, particles smaller than 0.1 microns are actually easier to catch because they have a lot of random motion that makes them bump into the filter fibers, she said.
“Even though coronavirus is around 0.1 microns, it floats around in a wide range of sizes, from around 0.2 to several hundred microns, because people shed the virus in respiratory fluid droplets that also contain lots of salts and proteins and other things,” said Dr. Marr. “Even if the water in the droplets fully evaporates, there’s still a lot of salt and proteins and other gunk that stays behind as solid or gel-like material. I think 0.3 microns is still useful for guidance because the minimum filtration efficiency will be somewhere around this size, and it’s what NIOSH uses.”
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