How to use N95 masks to protect against coronavirus?

"If I were wearing an N95 just for the weekly grocery store run, I’d probably be fine with alternating two carefully handled masks for many months as long as the elastic works and there’s no soiling. That’s not a lot of use! But if I were wearing one all day, every workday, I’d consider having one for each day and replacing them maybe every month. So that’s about five per month. Could one be really careful and make that two months? Probably.

But that brings me to the other problem: How are people supposed to find the right mask? I have purchased KN95s at local reputable stores and checked that they were included in the list of ones approved by the F.D.A. However, I would be careful about buying online, unfortunately. Too many fakes. I have seen reputable retailers like Costco beginning to sell N95s online again, and I would trust that. People can also purchase braces for surgical masks or make a brace themselves from a template, which really improves fit. Fit is very important for upping one’s mask game. We can start by noting that facial hair makes the fit worse, so shaving that beard for the pandemic is an option. (Sorry!) People can check the fit by adjusting the nose bridge to be tight and holding the mask and inhaling sharply, and seeing if they feel cool air coming in from the sides of the mask. The better the fit, the less the air from the sides. Preferably, there’s none. Also, my best-fitting mask does not fog my glasses at all because no air is escaping upward. When I get a new type of mask, I inhale and exhale while focusing to see if I feel if the air is escaping, or if there’s any gaping on the sides or around the nose area (my glasses fog to let me know of that)."