Uni Filter - Bf-1 Bf1 12 X 16 X 5/8 65-Ppi Green Fine FoamUni filter ATV air filters keep out all the dirt, dust, and mud providing superior engine protection. The principle of how foam air filters work is simple, open cell polyurethane foam is wetted with specially developed filter oil. The sticky filter oil.Features of Uni Filter - Bf-1 Bf1 12 X ..