Part of the definition of a virus when I was doing biology at university was that it was a non-filterable particle, Dave. It takes a lot more than a flimsy, leaky mask to stop a virus particle. Sure, your mask will trap snotty little droplets. Two things may then happen. The droplet will soak to the front of the mask then dry out, leaving free virus particles. But you'll feel nice and safe, even though your mask, which you'll touch unless you're a saint, is riddled with virus particles that will take off at the merest encouragement. Or your mask will stay soggy and, well, full of viruses, which you won't know about, and then you'll blithely do the wrong thing with it (shove it in your pocket next to your tenners, whack it on your dashboard, slip it down your chin until the next shop, save it for tomorrow...Unless you're a saint. I haven't seen too many of those. And of course you can behave badly with your mask and still not be a danger to anyone. In fact, that applies to the vast majority of mask wearers that you see. Why? Because they haven't bloody got it!