During the SARS pandemic back in 03/04 there was talk about wearing masks in schools, (I was a teacher in inner city Toronto). Problem is, that if you don't use them properly you are likely to infect yourself. You have to wash your hands properly, put on the mask using the elastic fasteners, don't touch the mask after, remove it using the elastics, dispose into a plastic bag lined garbage can, and then wash your hands properly again. Your eyes are not protected and a virus can enter that way as well. If you look at nurses when they are geared up, their whole face is protected.
The average person touches their face a lot. So don't touch your face or eyes and wash your hands frequently. N 95 masks are in short supply for the medical people, and unless you are sick, a mask may not be that useful in preventing viral transfer.
That said, the shop towel mask is pretty simple to make.