K&N's WRX & STI replacement air filters are designed to increase horsepower and acceleration while providing excellent filtration. K&N filters are custom designed to fit into your existing factory air box for simple, fast installation. K&N stock replacement air filters for street vehicles are covered by a Million-Mile Limited Warranty. K&N Filters use oil to provide filtration, and can be washed and recharged using the K&N cleaning kit (sold separately).

The Perrin drop-in air filter for the 02-07 WRX & STI uses a 2-stage foam filtration element to improve airflow in your stock air box; providing improved power and airflow while removing harmful particles from the incoming air. Using a special oil coating, the foam filter catches dirt particles while allowing air to pass unimpeded through the high-flow foam. This filter can be cleaned and re-oiled using the Perrin cleaning kit, sold separately.