Taken from Volant's page:
By using Donaldson's® PowerCore® Filtration Technology submicron contaminants load on the surface rather than collecting in the depth of the filter. This boosts efficiency and increases performance on your aftermarket air intake system. The filter media won't deteriorate as easily as traditional cotton/gauze filters. Plus, it's water resistant, so getting wet won't ruin your air flow or cause a decrease in performance. This is why we warranty our replacement air-filters for 4 years or 100,000 miles in urban conditions, whichever comes first.
Sorry 'bout that. I said water proof and should have said "resistant". This is the filter type that came with my Volant that I got last week.
Also from Volant site about the pre-filter:
The pre-filters are recommended when you install any of our CAS Cool Air Scoop or go serious off roading. It also benefits when your work truck is consistently around fine powder, sand or rainy weather. This cover protects the filter from splashes of water or saturating the filter in mud. The unique material contains uniform micron openings that filter out debris .005 or larger
If you click HERE
it'll take you to the page that I got this info from. Scroll down about half way to related products and you'll see pics too.