REI Watershed Cap
Here's what other sites are saying:
Designed for dedicated adventurers who aren't willing to let a little rain ruin their plans, the REI Airflyte cap with eVent(TM) fabric will keep your noggin dry. eVent fabric has a unique membrane structure that allows sweat vapor to escape to the outside of the fabric in one easy step. No matter how hard you work, overheating is highly unlikely due to this Direct Venting(TM) technology. CoolMax(R) polyester headband wicks moisture away from your brow and speeds the evaporation process. Reflective hits increase visibility in low light.