FilterSkins are a extremely thin but durable air filter cover.  While allowing maxium air flow, and oiled FilterSkin will catch 90% of the dirt that tries to pass through the air filter.  Between races or rides, simply pulling off a dirty FilterSkin and sliding on a clean one can save you time and money on solvents and oils.  Each package comes with 3 skins.  The skins are cleanable and reuseable.