Outerwears Pre-filters are constructed from a durable polyester material that is specially treated using a propietary hydrophobic process to repell 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 Outerwears pre-filters are proven to be extremely effective in repelling water, please keep in mind they are not water proof. If the filter is submerged in water, your filter can hold or pass water. This hydrophobic treatment will last for six months to one year, depending on use and conditions. * Filters out larger particles of debris down to .005 microns * Many larger debris particles simply bounce off * Hydrophobic manufacturing process repels water * Uniform micron openings allow air in and filters out debris and water Will adding a Pre-filter reduce my airflow or horsepower? 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. * Test results show no significant loss of airflow * Horsepower levels are maintained longer due to cleaner primary filters