A cooling idea from the folks in "The Land Down Under". The Watersorb site shows how to use polystyrene crystals to make cooling ties, vests, and helmets. Read testimonials on their site from service people in the armed forces who have found these useful even in the hottest of climates.
Although you can purchase the crystals from Watersorb, I wondered if there might be a cheaper source. I googled a few more sites, and...yup! You can use plant crystals. According to Debbie Colgrove at About.com Sewing , the crystals work great! (Debbie uses plant crystals from a gardening store.)
Hmm... I wonder if there are any reasons I couldn't use crystals from my local dollar store?