Here is a simple test you can do yourself, take your filter off after riding and a hard black surface,
tap the filter down on the black surface, don't let the filter bounce so the dirt/sand from the out side
will stay out side, slowly lift the filter up and see what is in the middle, the attached picture is my
filter after being washed 4 times, the filter was washed with the K&N filter cleaner then rinsed
allowed to dry a few days then whole washing process was started again, you should have
seen the amount of sand that was in ne middle before washing, I will take pictures after the next
trip to the dunes.



See the round spot of sand, that is the sand that came from inside the filter.

They will get washed and dried one more time before use, don't really matter since they are prefilters and the fresh K&N
oil should hold what ever dirt left behind in the filter?





Other filter is not as bad.





Yes that on the inside of the ring came from the inside of the filter hehe