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How Masks Protect Us from Covid-19

posted by Jason Kottke   Nov 02, 2020

How an N95 mask filters aerosols and droplets

The NY Times has a fantastic visualization on how face masks help keep us safe from catching Covid-19 by taking readers on a journey through a mask to see how they block aerosols and droplets.

A lot of the pushback around the efficacy of masks from non-scientists focuses on the size of the droplets and aerosols (super tiny) compared to the gaps between the fibers in the masks (relatively large). Intuitively, it seems like masks don’t stand a chance of stopping anything. But as this visualization shows, multiple layers of fibers do the job quite well. Masks don’t work like sieves, which will let every particle smaller than the holes through the mesh. Instead, imagine shooting a BB gun into a thick stand of trees — no one tree stands a good chance of getting hit by the BB but the forest will stop it eventually.

N95, KN95, and masks made from polypropylene have an extra weapon against particles: the fibers carry an electrostatic charge that attracts particles to trap them. Picture our BB flying through a forest of magnetic trees — it’s got a much better chance of being captured that way.

The visualization also touches on the importance of making sure your mask fits properly. The best masks fit tightly around the edges and include a space around your nose and nostrils. Masks with unfiltered valves should not be used — you’re just breathing virus out into the air. It’s been 8-9 months now that we’ve been dealing with the pandemic and there will be many more months of wearing masks. If your mask is fits poorly around your nose, your straps aren’t tight enough, you need to fuss with it after putting it on, have a mask with a valve, or (god forbid) are still just wearing a bandana, please please do yourself and others a favor and upgrade your mask. High-quality, well-made masks are much easier to find now than 6-8 months ago.1 If you can’t afford a proper mask, email me and I’ll buy you one. Masks are one of the most successful low-tech interventions we can do to prevent the spread of Covid-19, and the better our masks, the more effective they will be.

  1. I am hesitant in recommending particular masks because I am not a doctor or scientist, but you might want to look at Airpop’s masks. I also recently bought some Vida KN95s (but have not worn one yet). My daily mask is this Allett mask that combines a cotton layer with a non-woven polypropylene layer (I wouldn’t wear this on a plane for 4 hours but for 10 minutes in the grocery store in Vermont where community transmission levels are low, it’s fine). It’s more comfortable than a straight KN95 and fits my face perfectly — no “bunching up” gap between the ear loops or around the nose. Disposable surgical masks are very easy to find — they are better than wearing a bandana, valved mask, or even a thin cotton mask.