I too have noticed that about K&N. I have one that I don't run. I have the foam pre filter for it so that I can just take it off and have a fresh filter. But then I did a little research and purchased an AEM filter. The K&N website says it filter is 96% efficient. The AEM site says its filter is 98% efficient. To get appreciably better than that, you need a HEPA filter, which I don't think is practical for off road situations. I think the best testimonial for AEm is that Bobby Gordon ran an entire Baja 1000 on one filter by just shaking the dust out of it at pit stops.