K&N Airforce Pre-Cleaners are foam filter wraps designed to extend the service interval of K&N Filterchargers that are being used in very dusty conditions. Made from large, open-cell foam, Airforce Pre-Cleaners will stop 90% of the dirt yet restrict the filter's airflow by only 2%. They are made for use with K&N Filter Oil, and they must be cleaned with K&N Cleaner or soap and water.