Evaporative Cooling Vests These use the natural effect of evaporation to cool you down.  When these vests are placed into water the specially made non-toxic  material absorbs hundreds of times its weight in water.  This stored water is then slowly released.  In hot conditions, this water will start to evaporate.  As it does, the heat from the wearer is transferred into the air helping to reduce your temperature. Light weight. Easy to use throughout the day.  If it dries out all you have to do is submerge into water for hours more cooling. No electricity is required making them perfect for people on the move. The most affordable form of cooling vest. How does it work? Garments are made of a special fabric which holds the cooling energy for an extended period of time. Water causes a naturally cooling effect as it evaporates. Simply submerse in water for 1 to 3 minutes, or until garment reaches the desired level of hydration.  Gently wring out excess water and it's ready to wear! No freezers or cold packs necessary.  Once activated, the vest will provide many hours of cooling relief in low-humidity climates. Size Chest and Waist Circumference Range Vest Length* Weight Range Small* 34" to 36" 20" 50 to 100 lbs. Medium 38" to 40" 21" 110 to 175 lbs. Large 42" to 44" 21.5" 175 to 310 lbs. XL 46" to 48" 22.5" 275 to 360 lbs. XXL 50" to 52" 23.5" up to 400 lbs. * Length in front. Back is 2" longer. Polar Products Evaporative Cooling Vest