Portable and reusable, the non-electric Re-Heater Heat Pack, which contains sodium acetate, emits a moist heat that helps provide relief from stiff neck, backache, muscle soreness, hypothermia, and other situations. To use, simply press the activator, wait 15 seconds for the heat to spread throughout the pack, then squeeze until soft and pliable for maximum heat release (i.e., 130°F). To re-use, submerse the pack in a pot of water, either wrapped in a cloth or placed in a saucer or on a wire rack, boil for 20 minutes, then allow to cool to room temperature before re-using. It will also serve as a cool pack if refrigerated. Available in sizes ranging from 3" x 4" up to 12" x 20," depending on intended purpose. (8" x 16" neck-and-shoulder pack shown here.)