aFe offers three different types of filter media for most of our filters and intake systems because everyone has different driving conditions and different driving needs. There is the Pro5R, ProGuard7 and ProDryS. Without going into details of each media, the basically differences are: 1) Pro5R is 5-layers of progressively finer mesh oiled cotton gauze which offers maximum airflow. This media is ideal for those who drive mostly on paved street and highway who want maximum horsepower. 2) ProGuard7 is 5-layers of progressively finer oiled cotton gauze used in the Pro5R media backed by another 2-layers of finer porosity synthetic non-woven media which offers maximum protection. This media is ideal for those who do a lot of unpaved, off-road driving in severe dusty and dirty environments where protection is more important than maximum horsepower. This media is most popular with compression-ignition diesel truck owners. 3) ProDryS is a 3-layer progressively finer porosity synthetic non-woven media, which is oil-free and offers maximum convenience since it does not require re-oiling. This media is ideal for those who don’t want the hassle of re-oiling a filter.