Important re: masks during a pandemic: you may not want the same design you had for smog or (Californians...) fires.

A brief thread, but TL;DR: NO VALVES!

Fancier masks for air pollution have one-way valves to make it easier to breathe out. This is great when you're only worried about filtering incoming particles from the air because your exhalation can skip the mask material.

But this is TOTALLY WRONG for infectious disease.

In this pandemic, masking is at least as much about trying to stop your exhaled droplets from getting out as it is filtering incoming particles. A bypass valve completely defeats that goal!

So please, yes do mask up, but not with a mask with an exhale bypass valve.

(This thread inspired by a conversation with a fashion-forward friend who was thinking about modifying attractive mask designs with valves and hadn't thought of the downstream implications. And our joint realization that we've heard no one mention this.)