Filters and Filterskins are cheap, engine rebuilds are expensive. If you don't filter the dirt out of your air, your engine will filter the cash out of your wallet.
Filterskins are an extremely thin, durable air filter cover that allows maximum airflow while catching up to 90% of the dirt that would otherwise reach the filter — extending the life of each filter and making it more effective.
Between races or rides, simply pull off a dirty Filterskin to expose a clean filter underneath. It is like installing a new filter halfway through a long ride. Better yet, carry another oiled Filterskin with you and fit it out on the trail.