Off topic: information on the best materials and designs for masks which are homemade

As my family and I have taken to wearing masks when we go outside, as per the CDC recommendation, I have been researching information about the best designs and fabrics and filters to reduce the spread of coronavirus but also which might help keep out the virus. Most studies say that the N-95 respirator masks can only do that effectively. Others say that some masks can prevent incoming viruses depending on the fit and fabric. There are some new studies on the issue and more being done. The first question for me: are homemade devices safe and effective? The better studies suggest some designs and materials do help. However, a study published April 2 in The Lancet found that the coronavirus could survive on cloth for at least a day and on surgical masks for up to seven days meaning you have to be careful about cleaning or re-use.

In one study, homemade versions did prevent some microbes from getting through, suggesting the makeshift masks were better than nothing at all. The study co-author Anna Davies, a research facilitator at the University of Cambridge (U.K,) and a former public health microbiologist think that the right material and designs are better than not wearing anything. Researchers stress that lab studies test masks with no leaks or gaps. 

Lindsay Medoff, the CEO of Suay Sew Shop in Los Angeles, a clothing maker actually built a lab that could test particulate filtration down to 0.3 microns and tested a lot of different fabrics and filters, After significant work, they concluded that adding two blue shops towels and using a design that creates a tighter fitting mask blocked up to 95% of the particles they could test. Cotton masks blocked only 20% to 60%. The kind of shop towels they tested included the use of shop towels made from polyester hydro knit inserted into ordinary cotton masks which brought the filtration up to 93% of 0,3-micron particulates. They tested ToolBox’s shop towel and ZEPs Industrial Blue Knot.

Yang Wang, an assistant professor of environmental engineering at Missouri University of Science and Technology, recently worked with graduate students testing different combinations of layered materials.  Dr. Wang, based in Germany won an international award for aerosol research. He says that the best medical N-95 respirators filter out at least 95 percent of particles as small as 0.3 microns, whereas a typical surgical mask made using a rectangular piece of pleated fabric with elastic earloops — has been found to have a filtration efficiency ranging from 60 to 80 percent.

Dr. Wang’s group found that when common fabrics were used, two layers offered far less protection than four layers. A 600 thread count pillowcase captured just 22 percent of particles when doubled, but four layers captured nearly 60 percent. A thick woolen yarn scarf filtered 21 percent of particles in two layers, and 48.8 percent in four layers. A 100 percent cotton bandanna did the worst, capturing only 18.2 percent when doubled, and just 19.5 percent in four layers.

Dr. Scott Segal, chairman of anesthesiology at Wake Forest Baptist Health,  led a study which concluded that quilters tend to use high-quality, high-fabric count cotton. He found that best homemade masks were as good as surgical masks or slightly better, testing in the range of 70 to 79 percent filtration. Homemade masks that used flimsier fabric tested as low as 1 percent filtration, Dr. Segal said. The top designs were masks 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.

Most 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 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.

“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 of the minimum filtration efficiency … and it’s what NIOSH uses.”

Some say the best material to use is tight-weave cotton and that synthetic or polyester doesn’t work because of the virus’s ability to survive on those. A scarf doesn’t fit close enough on your face and so a mask is better.

Scarfs do not do as well as a mask as they fit closely to your face.