The two most popular filter media are the oiled Pro 5R and the oil-free Pro DRY S. Oiled filters generally offer higher flow than dry filters, and they require the maintenance of reoiling every time you clean your filter every 25-30k miles. The Pro DRY S allows you to skip the re-oiling step yet still offers increased airflow and protection compared to paper filters. aFe POWER oiled filters need oil to run properly. Never oil a Pro DRY S filter.