The Glacier Tek's RPCM Cool Packs are to be used with the RPCM Cooling Vest to help give you cooling power. These packs will stay at 59 degrees F for 2.5 hours. The packs can be recharged in water with ice in about 20 minutes, in the fridge or freezer, basically anywhere that is cool than 59 degrees F or 15 degrees C. These are the only PCM packs on the market without any poisonous or hazardous materials. The other cool packs on the market uses a petroleum based phase change but not this pack from Galcier Tek. These packs have Glacier Tek's technology that uses a natural, green formula. Great spare to keep around for your cooling vests!