https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3373043/

A cut t-shirt over your nose is actually quite good, so long as the pattern is somewhat tested. No, its no where close to an N95 mask, but even aerosol sprays can be somewhat mitigated with a simple cut t-shirt.

There are some internet studies suggesting an efficacy of 70% for T-shirts against 1-micron (bacteria) and 0.02 micron (viruses) particles. That's 6x worse than an N95 mask, but much better than unprotected.

EDIT: It seems like the flu (also a 0.02 micron virus) is primarily on water-droplets 5 microns in size. So we don't actually have to reach N95 mask levels for a major amount of protection, aiming at the 5 micron sized moisture bubbles is already going to help us severely.

Your argument about trapping virus inside the mask is not very convincing. If you are putting a physical barrier between your respiratory system and air in high-risk areas (general stores, pharmacies and public transportation), then statistically there should be far more prevented contacts with viruses than trapped virus particles.

The incorrectly fitted masks should provide some benefit over no mask, so this doesn't seem as a good argument for not wearing masks. I would think that even putting shirt over nose gives some protection as it prevents touching face and diminishes odds of contamination with spit particles. Besides, the article is about home-made masks and not N95 masks.

The only convincing reason against masks is that they give false sense of security, so they shouldn't be the _only_ measure. Washing hands, wearing masks and physical distancing can only be beneficial.

Where is that evidence?

"in medical facilities N95 masks are fitted specifically to individuals. You can't just throw one on and be protected. Most people won't go through the trouble of doing that properly."

Most people haven't been washing their hands properly either, and yet the government has gone to great lengths to educate people on how to properly wash their hands. There's no reason they couldn't do the same with mask fitting.

Lets not over-dramaticize N95 masks. An N95 mask is just 95% effective. Its not N99 or N100.

N95 is the relatively cheap and disposable mask. Its "custom fit seal" is the little metal bar that you push down on your nose.

Here is 3M's official fitting video. Its actually not very hard to use: https://www.youtube.com/watch?v=05wyH1-mLGk

Then elastic bands shove the mask against your face, forming an airtight seal. This can be effectively replicated with a decent hand-made mask solution (although the filtration of a hand-made DIY mask is much much worse, and completely untested compared to N95 designs)

Given the fact that we're in an N95 mask shortage situation, I think DIY home-made masks are the only solution for the general public. It just takes some scissors and a T-Shirt to make.