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 urea can be loaded into the envelope through the open top. Separate from the loading of the urea, a predetermined amount of ammonium chloride can be loaded into the envelope through the open top. The relative proportions of the predetermined amount of urea, the predetermined amount of ammonium chloride, and the predetermined amount of 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.
