Addendum 4/1: there’s even less reason now to make homemade masks as the CDC now allows non-USA rated masks (like KN95 or FFP2) to be used in non-hospital settings…
Exactly how good — or bad — are these homemade masks people are making? This is a deadly serious question, literally life or death. If you are wearing these it is crucial that you understand that a cotton mask filters only 50-70% of most virus particles. I do say “only” because I personally think this is an unacceptable risk, and the major problem here is a man-made shortage and a shocking lack of preparation. But yes, it is better than nothing. Hopefully within a week we will never need to have this discussion again, and healthcare workers will be using the N95 masks they deserve, all the time, as a one time use.
I have a list of N95 and PPE vendors here, direct from China, I would much prefer we all try to get real masks that way.
Otherwise, I would like to at least provide people with the evidence about homemade masks, even which fabric is best, in the rest of this article.
Can DIY Masks Protect Us from Coronavirus?
This very relevant question was nicely answered in one of two wonderful articles from the Smartair team, I’ve known them for years as we both done a lot of DIY research on air pollution devices like masks and indoor air purifiers. Here’s their take home message from their article, Can DIY Masks Protect Us From Coronavirus?
Data shows that DIY masks made with a single layer of cotton clothing or a tea towel can remove around 50-60% of virus-sized particles. This means they perform worse than surgical masks and FFP2 (N95) masks. Wearing the homemade masks for 3 hours had no significant effect on the filtration efficiency. DIY masks also work for children, but they are less effective on kids than they are on adults.
One study they quoted from 2009 compared no mask, to a homemade mask and surgical mask. The results: 0% for nothing, 50% for homemade mask, 80% for surgical mask:
Another group studied dish towels, literally not even cut, versus surgical mask and N95, even with 3 hours use the dish towel got ~65%, the surgical mask 78% and the N95 as awesome as ever at 98-99%:
What Are The Best Materials for Making DIY Masks?
Did you know some fabric is much better than others? Also, breathing easily through the mask is super important. This fascinating data was actually studied and again reviewed well in a Smartair blog, in their post What Are The Best Materials For Making DIT Masks? Here is their take-home message:
Test data shows that the best choices for DIY masks are cotton t-shirts, pillowcases, or other cotton materials. These materials filter out approximately 50% of 0.2 micron particles, similar in size to the coronavirus. They are also as easy to breathe through as surgical masks, which makes them more comfortable enough to wear for several hours. Doubling the layers of material for your DIY mask gives a very small increase in filtration effectiveness, but makes the mask much more difficult to breathe through.
Their most important graph is the list of fabrics and how they fared against 0.2 micron particles, which are virus sized. A surgical mask was best at 89%. In terms of t-shirt use, I was intrigued that a cotton blend at 70% was better than all-cotton at 51%. In terms of pillowcases, antimicrobial at 68% was better than regular one at 57%.
Breathability is also important, we can’t give people a mask they struggle to breathe through, even though it works more efficiently. A rock has a 100% filtration score, even after thousands of hours of use, get my point? For example, a vacuum bag was the most effective homemade fabric tested, but it was way too difficult to breathe through, and thus just isn’t practical to make. Here’s their graph showing breathability:
Are two layers better than one? They actually studied that as well! A double-layered dish towel worked really well, but also tested the worst in breathability, so in real-world terms it’s not an option.
My Bottom Line
Every healthcare worker deserves to have use of an N95 mask, at every visit with a sick patient.
If you must make a homemade mask, stick with the evidence: use pillowcases (not the anti-allergy ones) and 100% cotton t-shirts. And one layer is better than two in terms of comfort.
But please, please everyone, first let’s do our best to give healthcare workers the supplies they really need! We should not be compromising like this. Nor should this feel-good campaign distract us from the real shortfalls of our leadership.
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