The K&N PreCharger filter wrap is specially designed to extend the service interval of your K&N Filtercharger filter when used in very dusty conditions. They are made from durable polyester material containing a uniform weave. The PreCharger will stop small dirt particles with minimal restriction to the airflow of the filter. The K&N PreCharger filter wrap is specially designed to extend the service interval of a K&N air filter when used in very dusty conditions. They are made from durable polyester material containing a uniform weave.