Air-activated, one-time use. Advanced menstrual pain therapy. Patented heat cells for deep penetrating heat. Up to 8 hours pain relief. Soothing and long lasting pain relief. Odor free, discreet and stays in place. Questions? 1-800-323-3383. For most recent product information, visit www.Thermacare.com. Just open pouch, starts to warm on its own.