Caldera Hot/Cold Gel Pack The Caldera TherapyGel Hot/Cold Gel Pack provides relief for muscles and joints that are aching or sore. Can be applied either hot or cold (remains pliable when frozen). It is manufactured from a unique blend of plastics that allows it to be both pliable and reusable. The gel is latex free, non-toxic, and microwave and freezer safe. For use with Caldera Universal Hot/Cold Therapy Wrap #1080804.