I originally went with polyester, and while cool and brightly colored, I have and old cotton one that has faded to a pale torquoise, and has wrinkled to a uniform consistancy that I like to wear. I've found if it gets wet the cooling effect of the wind works better than polyester. So far no hassles other than a few strange looks. (PS I've only worn it from Veitnam to Bahamas).
The Sun has Risen on a New Day filled with the Promise of Adventure.