With masks sold out during the coronavirus outbreak, many people will have to make do with what some scientists have called “the last resort”: the DIY mask.
Data shows that DIY and homemade masks are effective at capturing viruses. But if forced to make our own mask, what material is best suited to make a mask? As the coronavirus spread around China, netizens reported making masks with tissue paper, kitchen towels, cotton clothing fabrics, and even oranges!
Researchers at Cambridge University tested a wide range of household materials for homemade masks. To measure effectiveness, they shot Bacillus atrophaeus bacteria (0.93-1.25 microns) and Bacteriophage MS virus (0.023 microns in size) at different household materials.
They measured what percentage the materials could capture and compared them to the more common surgical mask.
Not surprisingly, the surgical mask performed best, capturing 97% of the 1-micron bacteria. Yet every single material filtered out at least 50% of particles. The top performers were the vacuum cleaner bag (95%), the dish cloth (“tea towel” in the UK! 83%), the cotton blend shirt fabric (74%), and the 100% cotton shirt (69%).
The test above used bacteria that were 1 micron large, yet the coronavirus is just 0.1 microns – ten times smaller. Can homemade masks capture smaller virus particles? To answer this question, the scientists tested 0.02 micron Bacteriophage MS2 particles (5 times smaller than the coronavirus).
On average, the homemade masks captured 7% fewer virus particles than the larger bacteria particles. However, all of the homemade materials managed to capture 50% of virus particles or more (with the exception of the scarf at 49%).
Overall, the double layers didn’t help much. The double-layer pillowcase captured 1% more particles, and the double-layer shirt captured just 2% more particles. Yet the extra dish cloth layer boosted performance by 14%. That boost made the tea towel as effective as the surgical mask.
Looking at the data, the dish towel and vacuum cleaner bag were the top-performing materials. However, the researchers didn’t choose these as the best materials for DIY masks:
Instead, they concluded the pillowcase and the 100% cotton t-shirt are the best materials for DIY masks. Why?
The answer lies in breathability. How easy it is to breathe through your mask is an important factor that will affect how comfortable it is. And comfort isn’t merely a luxury. Comfort will influence how long you can wear your mask.
Fortunately, in addition to particle effectiveness, the researchers tested the pressure drop across each type of fabric. This gives us a good indication of how easy it is to breathe through each material. As a benchmark, they compared breathability of each DIY mask material to the surgical mask.
Although the tea towel and the vacuum bag captured the most particles, they were also the hardest to breath through. With two layers, the tea towel was over twice as hard to breathe through as the surgical mask. In contrast, the pillow case, t-shirt, scarf, and linen were all easier to breathe through than the surgical mask.
This article was published by Paddy Robertson Coronavirus, Masks on the 8th of March 2020. All credit & copyright belongs to the author & smart air filters.
