ThermalSoft Gel packs are double-duty packs. Heat them in the microwave for heat therapy. For cold therapy put them in the freezer. ThermalSoft Gel Packs stay soft, even at freezer temperatures and retain their hot or cold therapeutic benefits for extended periods of time. The large gel pieces mold to your body to deliver soothing heat or cold therapy. Two thin layers of vinyl make these packs sturdy yet conformable