It heals using the therapeutic power of heat or cold.
Heat therapy reduces muscle tension, so is particularly suitable for back pain, sciatica, muscle stiffness, and muscle and rheumatic pain.
Cold therapy, on the other hand, blocks inflammation in your body.
It's indicated for minor contusions, acute trauma, sprained, strained and twisted muscles, burns, bleeding, skin inflammations, insect bites, headaches, and toothache.

To use it hot, just heat it in boiling water or in the microwave;
to use it cold, just put it in the freezer before use.