Audi A4 2009, Magnum Flow Panel Air Filter (31-10181) by aFe. Filter Series: Pro Dry S. Constructed with 100Percent polyurethane on all four sides, this high flow inoil-freein OE replacement performance filter will outflow stock paper filter for improved horsepower and torque. Three layers of progressively finer mesh synthetic media provide maximum convenience and easy maintenance. Washable and reusable for multiple cleaning cycles, the tall open evenly spaced pleats provide excellent dust holding capacity for longer service cycle between cleanings. Integrated urethane bump seal insures tight, no leak seal over the life of the filter. In recent testing, this filter outflowed the factory filter by 31Percent.