Thermatek Heat Pack Refill - Set Of 4, Heat Pack Fits All Thermatek Travel Accessories Just open the pouch, shake heat pack to activate, and slide into the heat zone of any thermatek product to enjoy long-lasting, soothing comfort Includes 4 heat packs - 32 hours of heat inside Easy to use - air-activated, instant warmth. Safe, odorless, disposable after use, and comply with airline security screening restrictions Heat packs fit all thermatek travel accessories