Health officials in western countries have made an about-face in regards to their official policies regarding the wearing of face masks by the general public, in that they are now recommending that people do wear these items of personal protection equipment (PPE) to help prevent the spread of COVID-19. The wearing of face masks has been an intrinsic part of the health policies for countries in the east, and has been effective in helping these cultures’ efforts in protecting their populations against the pandemic.

First off, an important caveat on the subject: while face masks offer some protection, they cannot provide 100% protection against pathogens like the virus that causes COVID-19, and are not a substitute for social distancing and hand washing; masks are best thought of as a supplement to these practices, offering the potential to reduce an individual’s risk of spreading the disease.
 
“It’s not a decision to try to protect [one] from getting coronavirus,” according to CDC director Robert Redfield. “It’s to help modify spreading. And there is scientific data to show that when you aerosolized virus through a cloth barrier, you have a reduction in the amount of virus that gets through the other side.”
 
Additionally, it is being recommended that if members of the public have access to proper respirators, such as commercially-produced surgical masks or N95 respirators, that they do not wear them, but rather that they donate them to hospitals or other health care organizations so that the vital PPEs can be distributed to front-line health care professionals, thousands of whom put their lives on the line every day in environments with toxic viral loads.

Instead, the public is being encouraged to fashion their own face masks out of everyday materials, as the viral load outside of healthcare facilities isn’t nearly as hazardous. Toward that end, U.S. Surgeon General Dr. Jerome Adams has released a video demonstrating how to make an ad-hoc face mask out of ordinary materials such as a T-shirt, hand towel, or bandana, held in place by rubber bands. While not meant to be for everyday use, the simple technique could be a life-saver if you find yourself without a mask while facing a situation that might require one.

There are also numerous instructional videos that show how to make more permanent sewn masks, once again using the same materials described by Dr. Adams, but applying some basic sewing skills to the task.

One video, recommended by Toronto’s Michael Garron Hospital, shows how to sew a basic cloth mask, complete with pleating to allow the mask to form to the wearer’s face, and Business Insider offers an article that acts as a more in-depth guide to the DIY practice. These masks can be reused, provided they’re cleaned daily with hot water and laundry detergent. Harsh chemicals are not required for sterilization, as ordinary soap actively destroys viruses like SARS-CoV-2.

But what common household materials work best for a homemade face mask? Researchers at Cambridge University conducted tests on a number of materials for their effectiveness at filtering both bacteria and virus-sized particles, including (in alphabetical order) a dish towel, two types of pillowcase (antimicrobial and regular), linen, a scarf, silk, two types of t-shirt (100% cotton and cotton blend) and a vacuum cleaner bag; a standard surgical mask was tested as well, to provide a baseline to compare the effectiveness of these materials against.

The materials were tested using two different-sized particles: a Bacillus atrophaeus bacteria that averages 1 micron (that’s one millionth of a meter, or 0.001 mm), and a Bacteriophage MS2 virus measuring 0.02 microns across. For our purposes, the 0.1-micron SARS-CoV-2 coronavirus is ten times smaller than the bacteria-sized particles, so we won’t review them here (you can read an article discussing those results here), so we’ll just cover the results from the virus-sized particle test.

Unsurprisingly, the vacuum cleaner bag was the most effective at snagging the MS2 virus, filtering out 86% of the particles, and was second only to the surgical mask’s 89% effectiveness. This was followed by the dish towel (73%), the cotton-blend t-shirt (70%), antimicrobial pillowcase (68%), linen (62%), regular pillowcase (57%), silk (54%), 100% cotton t-shirt (51%), and the scarf (49%).

Although the materials were better at filtering out the larger 1-micron particles, the above results only averaged a 7 percent drop in effectiveness when tested against the 0.02-micron particles, despite the test virus being 50 times smaller. The SARS-CoV-2 virus, however, is five times larger than the MS2 virus, so these materials would presumably be somewhat more effective at preventing their passage than the test virus.

A third test was performed by doubling-up the materials, to see if twice the amount of fabric would be more effective. The results for the dish towel were the most promising, but yielded only a 14% improvement over the single layer; all other materials offered even poorer results, only showing a 1-2% improvement over their single-layer counterparts.

In the end, the researchers settled on recommending the pillowcases and 100% cotton t-shirt as the materials best suited for use in a DIY face mask: while the vacuum bag and dish towel were more effective as makeshift filters, they were also hard to breathe through, an important factor in affecting how long someone might be able to wear the mask. The breathability of the pillowcase and cotton t-shirt wound up being on par with the surgical mask; this breathability, combined with their respective filtering capacity, struck an appropriate balance for these materials’ use in a face mask.

This conclusion is backed by a 2006 article on improvised cloth respirators published by the CDC, using a “Hanes Heavyweight 100% preshrunk cotton T-shirt” that was “boiled for 10 minutes and air-dried to maximize shrinkage and sterilize the material.” The study found that although the improvised masks were insufficient in regards to established workplace standards, “this mask offered substantial protection from the challenge aerosol and showed good fit with minimal leakage.”

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