Instantly warm up the pack with the click of a little metal disc inside the unit. It is non-toxic and gives off heat up to approximately 130º F (54º C). This instant pack is portable and can be reused more than a hundred times. Reset the heat pad by placing it in a pot of boiling water until all the crystals melt back down to a liquid state. Excellent for muscle spasms, shoulder and neck pain and much more.