Robax HeatWraps with ThermaCare Technology's patented Heat Cells use controlled, deep penetrating therapeutic heat to provide back pain relief for up to 16 hours. By using a combination of ingredients that react when exposed to oxygen, the Heat Wraps are active for 8 hours, and you can feel the benefit of heat therapy for another 8 hours, for up to 16 hours of back pain relief. Robax Heat Wraps with Thermacare Technology also help relax, soothe and unlock tight muscles.