Honest question: Why do we need it to block _viruses_. Surely the virus isn't flying around with wings. Doesn't it travel on water droplets? Doesn't the mask do most of its good work by keeping water droplets in (or out)?
Generally the design and testing of the masks tries to take that into account.
I only looked into it informally during the early pandemic, so recollection is a bit hazy. But IIRC different amounts of virus travel on different sized droplets. Different sized droplets also can have different behaviors. Big enough and it doesn’t get through the mask. I think there’s also a “small enough” point where they don’t penetrate very well because they basically bounce around with brownian-like motion, don’t really create much flow. Also, IIRC larger droplets carry more viral load, but I’m pretty sure the smaller ones stay suspended in the air longer.
This varies from virus to virus; some generate droplets, some generate smaller particles ("aerosols" / airbone transmission). Measles is so infectious because it travels in smaller particles that linger in the air longer.
However, it doesn't matter how good the N95 material is if the virus travels on a water droplet _around_ the mask. This is what all the comments about fit means.
IIRC Covid is airborne so it doesn't need to travel on droplets.
But feel free to double-check that one. Everything surrounding Covid is so tied to politics and identity, it's easy to get things mixed up between actual studies that have actually demonstrated a thing and people just spouting off whatever just came out of their assholes.
In other words, I believe I read an article on how we know now that Covid doesn't need droplets to transmit, but it honestly could have just been someone saying that there was an article claiming that and I've just conflated being told there's an article with actually reading the thing.
I only looked into it informally during the early pandemic, so recollection is a bit hazy. But IIRC different amounts of virus travel on different sized droplets. Different sized droplets also can have different behaviors. Big enough and it doesn’t get through the mask. I think there’s also a “small enough” point where they don’t penetrate very well because they basically bounce around with brownian-like motion, don’t really create much flow. Also, IIRC larger droplets carry more viral load, but I’m pretty sure the smaller ones stay suspended in the air longer.
It is a pretty complex space I think.