just my two cents on this, i`ve read alot of discussions on this from all the pros here, and they say foam is the way to go, but i and all my friends with shees have been using k/n`s for years with no adverse effects. it`s all coal strippins, the dust is so fine its like baby powder, i hate even breathing it, but our top ends last 3 to 4 seasons and we ride alot. we all use outerwears too, after one hard ride the outerwear will be plugged up, just shake it off and good to go again. by the second ride we have to clean the filter.