The Science behind the cold pack

The cold pack is actually filled with ammonium nitrate and water. The reactions of the two elements causes an endothermic reaction. An endothermic reaction means the reaction absorbs heat from the surroundings. When you hit the cold pack, it breaks the tube so that the water mixes with the fertilizer. This mixture creates an endothermic reaction -- it absorbs heat. The temperature of the solution falls to about 35 F for 10 to 15 minutes.