This self-activating hot pack is very unique. To activate, bend the red bar and the pad will heat up to 54° C within seconds. It remains hot for hours. This heating pack is liquid and transparent prior to use, but becomes white and hard after having been activated. To reactivate the self-heating element, place the pack in boiling water. Then heat it for approximately 15 minutes or until the liquid in the pad turns completely clear. Allow the device to cool before using. Measuring 20 cm x 40 cm, this pad can be reused up to 500 times.