The ONYX COOL Back/Hip features a plant-based cooling phase change material (PCM) in a wearable therapy for back, hip and belly pain. This wearable therapy is available in two temps: ONYX COOL Back/Hip - 58° Chill: designed for cool therapy and pain relief. May be used to treat sports injuries, pregnancy back and belly pains, and to help heal tissues after back or hip surgeries and C-sections. This cool (not too cold) device is safe to wear directly on the skin without risk of ice burn, frost bite or vasoconstriction. ONYX COOL Back/Hip - 80° Go: designed for on-the-go cooling comfort and “right now!” relief for sore muscles, aches and pains. The plant-based phase change material feels surprisingly cool for an hour or more, depending on ambient temperature and use. It refreshes to cool state when not in use; no refrigeration needed.