HEAT PAX AIR ACTIVATED BODY WARMER

Per the manufacturer: The warmers all have a shelf life of at least 3 years. There is an "expiration date" on each warmer that is 3 years out. However, the warmers do not go bad, like a gallon of milk, once the expiration date is reached. 3 years is just the minimum time it usually takes for air to penetrate the outer film packaging and begin effecting the warmer. The longer after that date passes the shorter the heating duration will be. For instance if you have a warmer that is a year passed the expiration date it may last for 10 hours verses the 20.