[NTF6]

All filters will allow some dirt through regardless of the type, you might not see it but it's there. From my dirt bike days (only a few years ago), it didn't matter what brand of air filter or brand of oil and ride around some of the dustiest tracks for a few hours, pull the filter, shine a torch into the airbox and then wipe your finger down the inside and see the difference...huge. Micro dust particles and heaps of it. You don't see that in your cars simply because you don't spend a day thrashing around a dusty motocross or desert enduro track but it is still getting through.