They are made from the same material as the filter ones. It is an exremely fine mesh. Small enough air flows through easily but water will bead. Its not water proof, its water resistent. If it gets cloged that bad while riding, it is it held on with velcro. You can just wash it off in a stream. It is good to have, other wise all that crap will go into the box, and then on your filter, and that would be a pain in the ass to clean. Here is the FAQ on Outerwears from their website. I think it will help clear up any other questions you may have. Outerwear FAQ
And this is the oil I recommend. It works very well.
PJ1 filter oil