the more dirt that cakes on the outside the finer the dust/dirt it filters with out decreaseing the air flow thru it

more dirt caked on the outside = 1000s more finer air passages thru the filter media the air goes thru

you cant see thru mine right now,thats for sure

now if you let it dry out I could see it not filtering very well

the oil is not gonna let any dust thru if it is kept properly oiled

read the box on theory of operation on how it works,it is to be oiled more often if it is in a real dusty service area and heat will dry it out

so it does need to be serviced from time to time

where I am here in Fl we have lots of dirt roads and dust...paper filters dont cut it every 2 months and mpgs and performance fall right off on mine when the go from white to gray on the paper media

which when I added it up was 100$ a yr x 10 so far thats 1000$ I would have spent...just on air filters...

so 40$ on the K&N 1x and a recharge kit for 10$ 1x for 2 cleanings and 5+ oilings

and it been 10 yrs now = 50$

I have saved a few bucks in the long run,IMHO

to each his own,if it wears out from it not working I will build another and press on with the same 50$ worth of reusable filter

agian just my worthless

to all the K&N haters