Air-activated, one-time use. Advanced neck pain therapy. Up to 16 hours pain relief. Clinically proven to relax tight muscles and enhance flexibility & mobility. Provides up to 8 hours or heat while you wear it plus 8 hours of pain relief after you take it off. Odor free, discreet and stays in place. Patented heat cells for deep penetrating heat. New design for improved fit! Questions? 1-800-323-3383. For most recent product information, visit www.thermacare.com. Just open pouch; starts to warm on its own.