Plastic sheet can be heat-sealed to form a water-tight envelope having an open top. A water-tight frangible container can be loaded into the envelope through the open top. The water-tight frangible container can contain a predetermined amount of water. A predetermined amount of phosphate ammonium nitrate (PAN) can be loaded into the envelope through the open top. The relative proportion of the predetermined amounts of phosphate ammonium nitrate to water can be selected to provide a target cooling effect to a portion of a body to which cooling is to be applied. The open top of the envelope can be heat-sealed to form a water-tight outer pack.
