N95 masks - there are different models, and plenty do not have the valve.
T-shirt - multi-layered-panels - has some efficiency, but is of course not “perfect protection.”
Using any mask, requires proper handling and maintenance -— but some people cannot be bothered.
Most people have no idea, and why would they? Geez, how well does it work when you throw people a ton of PPE with no training, which is usually how the military rolls. “Here it is, figure it out.” Google “Ebola Africa” if you want to see how people dress when they’re concerned about disease. They pretty much wear a full-body condom. Some mask made from a t-shirt is just as effective? Rrriiigghhhtt! This is as bad as the Israeli civilians running around in shorts, T-shirts, and gas masks when Saddam was popping off scud missiles at them and there were concerns of them being tipped with chemical weapons. (And actually, they had no worries. If Saddam had popped off chemical weapons at Israel, they would’ve removed Baghdad from the face of the earth.)