Outerwears Pre-filters contain uniform micron openings and are run dry meaning no additional oils or additives are required. Running a dry Pre-filter means there is no dirt sticking to the oil creating premature loss of airflow and horsepower. Only those particles of dirt smaller then .005" get into the actual air filter, the larger particles simply fall off the Outerwears pre-filter. In addition, Outerwears Pre-filters are constructed with a woven mesh that is specially treated at the mill using a proprietary process to repel water. This hydrophobic water repellent process is not sprayed on; consequently, there is no airflow loss. Whether you use your vehicle for everyday driving or for hard core off -road racing, Outerwears Pre-filters will work for you to protect and extend the life of your performance air filter and engine. Although our pre-filters are proven to be extremely effective in repelling water, please keep in mind they are not water proof. If submerged, your air box can hold or pass water. This hydrophobic treatment will last for six months to one year, depending on use and conditions.