Overview The K&N PreCharger® is a specially designed filter wrap made to extend the service interval of your K&N Filter when used in very dusty conditions. They are made from durable polyester material containing uniform micron openings. The PreCharger will stop small dirt particles; yet add little restriction to the airflow of the filter. The PreCharger is designed to be run dry and can be cleaned with K&N Filter Cleaner. The PreCharger is custom made to fit each application. Double stitched elastic openings assure that the PreCharger will stay in place.