I've never seen those, but now I might have to pick one up. I've been using a cheap wallet like thing I got at on of those teenybopper accessories store (Icing or Topkapi). I figured whatever they had would be made out of some plastic-y sweatproof material. I've heard of people using the holders especially made for fishing licenses also--again they're water/sweat proof.
"Bicycling is a big part of the future. It has to be. There's something wrong with a society that drives a car to workout in a gym." -- Bill Nye