I have had these filters for over 8 months now. I just cleaned them the other day. I don't see any dirt or coarse debris like with a regular disposable filter. When I washed the filter with a hose, I couldn't find anything coming out either. The benefit of using these filters is that I can reuse them instead of adding them to our garbage output. I didn't have to buy filters and throw them away, so I like the concept, but only if it works. Then I went and bought a regular disposable filter. I have two return air intakes on my air conditioner. I have a K&N filter on one side and a regular disposable filter on the other. After over 4 months of normal use I have tested the filter and of course I can say that the disposable filter has trapped dust/dirt proving that it works. I checked out the K&n and it looks the same as the day I first took it out of the box. I know it's not 100% conclusive evidence but it's a sad day for this guy to say that k&n may leak more air but in this case I don't think the dust/dark capture is, which I believe and means I'm back to using disposable filters.
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