Robax® Hot Packs with ThermaCare® Technology feature patented thermal cells that provide controlled heat that penetrates deep to provide up to 16 hours of relief. Thanks to a combination of ingredients that react when exposed to oxygen, the warm compresses work for 8 hours and you can experience the benefits of heat therapy for 8 more hours, for back pain relief that lasts. until 4 p.m. Robax® hot packs with ThermaCare® technology also help relax, relieve and loosen tight muscles.