China (Mainland)
It is a non-electronic hot pack and equipped with a metal disc inside. When bending the metal disc, the liquid will turn to crystal and release the heat to 50 oC. It will keep warm for 40 minutes approx. To reactivate it, please put it in a pan of water and bring to boil for 10 - 15 mintues or until the crystal completely returns to liquid status. Take it out and cool down to room temperature for next use.