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What Makes a Good Mask? Let's Uncover the Facts

There's a whole lot of talk about masks these days and they seem to be popping up everywhere for purchase. But is there a secret to a good mask? Are some better than others?

This article was first published in The Montreal Gazette.

Given that face masks will soon become mandatory in enclosed public places, a reader recently sent me an email asking a very important question. What makes a good mask? Surgical masks coupled with a face shield are now standard in the hospital when we interact with patients. But while surgical masks are not expensive, they are single-use devices and those costs add up over time. Cloth masks can be re-used and are therefore more economical long term. They merely need to be disinfected between each use, which can easily be accomplished by throwing them in with the rest of your laundry.

However, one wants to make sure the mask is actually effective. The key to a good mask is first the fit. A mask needs to cover your mouth and nose to be effective and should provide a relatively snug fit against your face, being neither too loose nor too tight. Large gaps between the edge of the mask and your face will drastically limit its effectiveness, and a mask is all but useless if your nose is sticking up over the top or you tuck it under your chin. A wire or ridge on the nose piece can help mould the mask over your nose. This serves the dual function of providing a better fit and preventing your breath from fogging up your glasses.

But independent of fit is the question of fabric. Both Health Canada and the CDC have guidelines on how to make your own mask and provide both sew and non-sew techniques for those who are not adept at handling needle and thread. They both recommend a two-layer mask made of a tightly woven fabric like cotton.

Though evidence testing different types of fabrics for masks is limited, what evidence exists does provide some insight. Researchers have found that while homemade masks do not match the filtration efficiency of surgical masks, masks made of cotton, cotton blends or pillowcases performed better than fabrics like silk. Masks made out of tea towels or vacuum cleaner bags were also tested, and while they provided good filtering capacity in theory, they ended up being impractical and unusable in terms of fit and comfort. Masks must, after all, be comfortable and provide a good fit, and the stretchiness of cotton fabrics seemed to make them the best material for this purpose.

These researchers and others have also found that using two layers of fabric improves filtering efficiency for cotton masks, hence the Heath Canada and CDC recommendations to use two layers of fabric. One might then ask if three layers would not be better than two or whether one should leave a pocket between the two layers for a paper towel or coffee filter. There are, to my knowledge, no studies testing this practice. Intuitively more layers probably do add some protection, though at the price of comfort and breathability. Thus if extra layers make a mask so uncomfortable that people will not wear them, then they have failed in their purpose.

While filtration efficiency can be measured in a laboratory, there is sadly no easy way to assess that for the general public. However, if a two-layer mask is made from fabric with a reasonably high thread account, then it should perform adequately. Fabrics sheer enough to be transparent are probably not ideal and if you can blow out a candle while wearing your mask, it is likely not good enough. These are not scientific standards but may serve as good rules of thumb.

The great problem with regard to masks, though, is not quality control; it is that many people either refuse to wear them or wear them inappropriately. If we could get everybody to wear a mask in public settings, then it would help reduce the spread of the virus. Masks by themselves will not stop the virus entirely, but they will help, a little. And in a pandemic with thousands of deaths, a little goes a long way.


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