Adding a third layer to cloth face masks is now recommended for preventing the spread of COVID-19. Non-woven polypropylene fabric is the material of choice for this third layer, but many people may ...

A version of this story appeared in Volume 98, Issue 25 It’s important to consider all these parameters when determining what materials to use for a mask, says Yi Cui, the Stanford materials scientist ...

01/28/21 Update: This article describes the benefits of filtration in homemade masks, which are similar to the protection afforded by the surging practice of double-masking. You can read more here.

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