Keeps your body cool on the hottest days. Terrific for Tennis, but also great for other sports, hiking, walking and working around the house and garden. Just soak in water for 10 minutes, and crystals expand 400 times and turn into a cooling gel that promotes cool air flow. Wrap around neck or tie on as a head band. Crystals stay active for up to 2 days. 100% safe and non-toxic. Rinse in cool water and air dry to clean. Way-Cool!