Can be used hot or cold. They provide moist heat and soothing cold. Stays hot or cold for 20-40 minutes. They are covered with a four-way stretch material which allows maximum conformity, heat transfer and comfort. Remains flexible and soft at temperatures as low as -20°F. Does not leak, even if punctured. Microwavable or can be heated in a conventional oven. Guaranteed for six months for manufacture defects.