Donaldson P-Series Air Filters Donaldson air filter media is made up of specially formulated fibers designed to trap contaminants such as dust, dirt and soot before they reach the engine. The media is pleated to maximize the filter surface area and placed between rigid liners to provide stability and. support. A high quality filter seal is applied or built-in to the open end of the filter to prevent dirty air from bypassing the filter. Donaldson has developed an extensive range of air filter media to provide the best engine protection no matter what the operating conditions. For example, using the same particle size contaminant, for every eight grams of dirt passed through a Luber-finer filter, the Donaldson filter passed only two grams.