[murgindrag]

My impression is that there are rapidly rising and then diminishing returns on investment.

Going from cloth to any mask with a high filtration layer is a huge improvement. Cloth is <30% of small particles. High filtration layer is >90%. Beyond that, the benefits are questionable.

Some surgical masks include a non-woven layer, and those already do pretty well (but how would you find those? pre-COVID it was easy). From there, genuine (non-counterfeit) KN95 and nanofiber masks are a big step up, and incredibly effective. At least pre-delta, if everyone used those, combined with modest social distancing, there was very little spread.

N95 masks are a modest improvement from there in terms of filtration, but by that point, mask quality (at least pre-delta) no longer appeared to be the dominant risk factor. COVID19 can spread through other mucous membranes (e.g. eyes). While combined with a face shield, used correctly, etc. I'm sure N95 make a difference over KN95, in practical public health use, I doubt there's any difference.

This is a good summary of data:

https://docs.google.com/spreadsheets/d/1M0mdNLpTWEGcluK6hh5L...

https://docs.google.com/spreadsheets/d/1i06OAItoOwIUaMjElr8m...

I don't really distinguish between things with >90% filtration. Unless you've got an excellent seal and are otherwise protected, it doesn't matter much. Note that the measurements are performed at 300nm. There isn't much spread at 300nm (a single virus particle is unlikely to make you sick). A 90% mask at 300nm will have >>>90% at e.g. a micron. A micron particle is unlikely to have more than one or two COVID particles (a micron is 5 COVIDs wide).

I do distinguish based on pressure drop. Lower means more air goes through the mask, rather than around.

I also do distinguish based on technology. The nanofiber ones don't degrade the same way as N95. The N95 nonblown layer will theoretically beat nanofiber for the first couple of hours of use, but once it's moist from your breath, nanofiber beats it. Personally, I use a disposable nanofiber mask, and I consider it a better (e.g. safer) option. I'm not in a controlled cleanroom/hospital setting, and life happens. Masks do get reused, abused, rained on, and generally exposed to life. Nanofiber have much better durability.

I also supply chain. Amazon and eBay are rife with counterfeits. I like masks where I can order direct. Especially 3M tends to be mostly fakes, unless ordered through authorized distributors.

I distinguish on fit. In addition, a well-fitting 90% masks beats a poor-fitting 99% mask, since with a good fit, all the air goes through the mask. Order yourself a variety pack and see what's comfortable and fits.

The biggest thing you can do is limit yourself to settings where everyone uses reasonable precautions. All parties wearing KN95 masks, having reasonable social distancing, favoring outdoors, vaccinated if >12, etc. is pretty safe. If you have a mixture of extreme precautions and no precautions, everyone is at risk.