With fabric stores closed for the pandemic, crafty consumers have begun scavenging around the house for potential materials to make their own masks. What about using denim jeans? Or bras?
D.I.Y. mask makers have learned that you can make a mask out of pretty much anything, from paper towels to men’s boxers. But whether the material will be breathable and filter out microscopic particles is another question. At particle testing labs around the world, high-tech air quality testing equipment now is being used to measure the filtration potential of coffee filters, sweeper pads and whatever other unconventional mask material home crafters can conjure.
This week, a Beijing-based engineer used a laser particle tester on 30 everyday materials based on crowdsourced requests by online readers. Paddy Robertson, the chief executive of Smart Air, which makes air purifiers, has gained an online following for his blog posts on masks, which explore such topics as whether microwaves can disinfect face masks or paper towels can be used as filters.
“We started getting people asking us, ‘Have you tested this?’ and ‘Have you tested that,’” said Mr. Robertson. “I’m working around the clock to try and answer more of these questions. We’re really happy to be able to help.”
In addition to Smart Air, researchers from Virginia Tech, Missouri University of Science and Technology and Wake Forest Baptist Health have stepped in to test everyday mask materials. Some data has also come from a 2013 report from University of Cambridge researchers on homemade masks. The studies mostly compare mask filtration to the industry standard of 0.3 micron particles — the toughest particle size to catch. Some reports look at larger particles.
The problem with all of the studies is that there is tremendous variability in fabrics used in T-shirts, jeans and pillow cases. Even disposable shopping bags and paper towels come in different materials and weights. While you may not have access to the exact fabric tested, the research can give you guidance.
For comparison, the N95 mask, which should be saved for medical workers, filters 95 percent of 0.3 micron particles. A rectangular surgical mask filters between 60 to 80 percent of those particles. While simple fabric masks don’t test as well, studies show that homemade masks still can help stop the spread of viral illness and offer adequate protection for people practicing social distancing, even if a mask is capturing a lower percentage of small particles.
When in doubt, hold fabrics up to a light to compare how much light filters through: The less light, the better. Test the fabric to make sure that you can breathe through it before turning it into a mask.
From all the tests, a few things stand out. In general, a lot of everyday fabrics do a good job filtering larger viral particles and respiratory droplets (the type many of us would encounter by a person sneezing or coughing nearby). Everyday fabrics are less effective at filtering very small particles, but in the lab setting, some homemade mask materials can rival a standard medical mask for filtration efficiency.
In most cases, natural fibers performed better than synthetic ones, and two layers are better than one. Some items, like vacuum bags and coffee filters, do a good job of filtering but can be tough to breathe through.
It’s important to remember that any face covering is better than nothing and will protect others from your germs. Whether a mask protects the wearer from incoming germs depends on how snugly the mask fits around the face and the quality of the material used.
Here’s a roundup of the latest material testing results, along with earlier findings.
Denim and canvas: In the Smart Air report, denim and canvas filtered more than 90 percent of large particles and about a third of small particles. This video shows you how to make a no-sew mask out of jeans and a scarf. If you can sew, The Times Style section has provided instructions for a simple mask pattern that can be downloaded.
Bra pads: Bra pads vary, but the rounded shape can resemble a traditional medical mask, and they come with elastic straps, which is why some people are turning them into face masks. Smart Air said it tested a “muslin and sponge” bra pad that captured 76 percent of large particles and 14 percent of small particles.
Paper towels and shop towels: A lot of people are using disposable towels to make a simple mask or to add as a third inside layer to a fabric mask. In the Smart Air test, paper towels (two layers) filtered 96 percent of large particles and 33 percent of small particles. Blue “shop” towels, an absorbent disposable towel often used by mechanics, filtered 87 percent of large particles and about 19 percent of small particles. We added a paper towel to our homemade T-shirt mask.
Reusable shopping bags: Smart Air tested reusable bags made out of nonwoven polypropylene. The bags filtered 73 percent of large particles and 11 percent of small particles.
T-shirts: Cotton T-shirts are by far the most popular do-it-yourself mask fabric, but there is a lot of variability in T-shirt materials and how well they perform in lab tests. A stiff, uncomfortable T-shirt is probably going to do a better job than a lightweight, more breathable one. At Virginia Tech, a single layer of an old cotton T-shirt captured 20 percent of particles down to 0.3 microns. It captured 50 percent of larger particles. A 2013 University of Cambridge study found that two layers of T-shirt captured about 70 percent of larger particles. In the Smart Air test, two layers of T-shirt captured 77 percent of large particles and 15 percent of small particles.
Tea towels: Smart Air used what it called a “kitchen towel” and found it filtered most large particles and 48 percent of small particles. Tea towels became a popular source of mask material after an August 2013 study from University of Cambridge researchers found the tightly woven absorbent material, which was not terry cloth, compared well to a medical mask, but the study authors did not note the brand.
Pillow cases and sheets: Smart Air tested 100 percent cotton, 120-thread-count sheets, and found the material filtered 90 percent of large particles and 24 percent of small particles. In the 2013 study, two layers of pillow case fabric tested close to the efficiency of a surgical mask for large particles. The Missouri scientists reported that four layers of 600-thread-count pillow case material achieved the filtration protection of a surgical mask.
Cotton sewing fabric: A two-layer mask of flannel and cotton was one of the best tested in the Wake Forest Baptist study and rivaled the efficiency of a surgical mask. In general, the high-thread-count cotton fabric preferred by quilters for its durability does a good job of filtering particles.
Scarves and bandannas: There is so much variation in scarf material, the light test is probably your best bet. Most cotton bandannas are made with very lightweight cotton and, even when folded over four times, don’t offer much protection. In the Smart Air tests, both performed poorly.
Coffee filters: Coffee filters have mixed results. While they test well, some filters aren’t very breathable. The best bet seems to be a thin, basket-style coffee filter inserted between cotton layers.
Disposable floor sweep pads: Some people are making masks out of disposable sweep and mop pads. Smart Air tested a thin disposable floor cloth which filtered only 7 percent of small particles, but a thicker pad might do better.
Air filters and vacuum bags: Scientists trying to find effective alternative mask materials for medical workers have cut up layers of air filters and tested HEPA vacuum bags. Both can work quite well, but both have significant downsides. Air filters, when cut up, can release fibers that can be dangerous to inhale, so the filter material should be sandwiched between layers of heavy cotton fabric if used in a mask. Vacuum bags are good filters but not that breathable. Plus, some brands of vacuum bags may contain fiberglass so should not be used to cover your face.