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. Adding an Outerwears Pre-Filter will not have any significant reduction in airflow (independent lab test results available upon request). Most Performance air filters allow more air in than the engine can actually handle. In fact, an Outwears pre-filter keeps your primary filter cleaner for a longer period of time allowing your engine the ability to sustain its original airflow and horsepower for an extended amount of miles and time. Many of our customers claim they have also noticed an improvement in fuel efficiency. This may simply be attributed to the fact that they are keeping their air filter cleaner.