Has to be. The whole point of the K&N is to flow more air/less restriction and to achieve it, you get less filtering efficiency. The oil acts as a filter across the large voids in the cotton gauze. So round and round we go....a trade-off analysis of how much less is the efficiency for the added flow and does it make any meaningful difference in your engine's performance and wear. There is no reason for average drivers to use one of these over throw-away OE-style paper filters that you may change 3-4 times over an average ownership run.