I believe in all the dust I see into my carbs and the airbox when I've used K&N or JR (france brand like K&N).
I've used foam whenever I've found one for my application. And K&N/JR/BMC when I didn't find a foam filter.
To have the same performance of a K&N the foam needs to be kept clean. And I clean it every 3 months or 3000mi.
