Think of it like a sponge and some dye.Sorry to bring this back up, but I've been thinking about it. Wouldn't the above only apply to someone who already has the virus? What worry do healthy people have to have of contaminating their own face masks, and wouldn't it then act to mask some flu particles out in the unlikely case that a person wearing it is coughed around. I am aware of the fact that face masks do not provide 100% protection, I remember some doctor saying "they're useless, their only advantage is to create awareness of the disease." I disagree with this - they would provide some measure of protection, not that I'd wear it anyway though; wearing one equals social suicide imo xD.
If the sponge is dry and some dye is thrown onto it, it wont sink into the bottom of the sponge.
If it is wet, the dye would travel down to the bottom using the water as a highway.
S.H.O.D.A.N. wrote it more technically.