A flameless ration heater, or FRH, is a water-activated exothermic chemical heater included with Meals, Ready-to-Eat (MREs), used to heat the food. US military specifications for the heater required that it be capable of raising the temperature of an 8-ounce (226.8 g) entree by 100 °F (56 °C) in twelve minutes, and that it has no visible flame.