Abstract: An activator (10) made in accordance with the principles of the present invention includes activating crystals (11) that have been formed into a shape and then coated with coating (12). The activator (10) of the present invention can be used in any environment in which the solidification of a supercooled solution occurs and whereby heat is generated during the solidification process. In the preferred embodiment disclosed herein, the activator is placed inside a hot pack (15) containing a supercooled solution (16). The hot pack can be made of a container made of a thermoplastic film which is formed into a bag, filled with activator (10) and the supercooled solution (16), and sealed to form the hot pack. The coating (12) of the activator (10) is impervious to the supercooled solution (16) in the hot pack (15) and into which the activator will be placed. The supercooled solution (16) may be any of a variety of chemical compositions known in the art which give off heat as they solidify.