Outerwears Pre-Filter for K&N HA-4099 Filter - Blue 20-1008-02Outerwear pre filters are manufactured from a durable polyester material Material contains uniform micron sized openings that allow air in, yet filters out the unwanted elements, such as sand, dirt, clay and even water Filters items as small as . 005 in diameter without noticeable air flow restriction Dyno and flow bench testing has shown no significant loss of horsepower or air intake while using this product Silicone impregnated micro mesh is water