Water activated, each heavy duty bag will heat several retort pouches. Remove retort from box and put into heater bag, add water and close bag, in 10-15 minutes you have a hot (about 140(0)F) meal. MRE heater bags must be used with caution. DO NOT USE THE WATER after you have activated the heater. Do not re-use heater. Please dispose of properly. An excellent way to get a hot meal even in the harshest of conditions. Weighs.98 lbs. for 12. Sold in 12 pack.