The AIRAID Pre-Filter is highly recommended for use over your AIRAID premium air filter in extremely dirty environments. The AIRAID Pre-Filter is manufactured from a durable water resistant polyester material and helps to support longer service intervals for the AIRAID washable air filter that the pre-filter protects. With uniform micro openings that filter out debris 5 microns and larger, the dyno & flow bench testing has proven no significant loss in power or airflow using this product.