The Serenity Gel Hot/Cold Pack can be used as a hot or cold compress. For hot compress, please put in a microwavable container and cover completely with water at medium power setting for 30 seconds intervals, until reaching the required temperature. Or soak into hot water approximately 80-90 degrees C / 170-190 degrees F for 3-5 minutes. For use as a cold compress, please place in the freezer for 2 hours. Each pack has printed instructions on the back.