I just ordered a UNI from Rocky Mountain ATV for my 2001 XR. I thought it was interesting that the UNI comes with a replacement filter cage.
The UNI spin sez:
The Uni Air Filter is two layers of foam that will trap small and large particles like dust and dirt helping prevent anything reaching to the cylinder. Uni Air Filter is manufactured of high performance foam and biodegradable. The Uni Air Filter has a seamless design that allows for a maximum amount of air flow to your machine. The Uni Air Filter is easy to clean with the Uni Air Filter Cleaning Kit and will help cut the grease and oils down so you are able to reuse indefinitely
MULTI-STAGE COMPETITION OFF-ROAD AIR FILTERS.
Traps dirt and dust in two layers of foam, the large pore pre-filter captures the bigger particles.
The small pore inner filter prevents any engine wrecking grit from reaching the cylinder.
Comes with a replacemnt filter cage.