Self-heating food packaging (SHFP) is active packaging with the ability to heat food contents without external heat sources or power. Packets typically use an exothermic chemical reaction. Other types of active packaging are self-cooling food packaging and radio-frequency identification (RFID). Packages like these are useful for military operations, during natural disasters, or whenever conventional cooking is not available. These packages are often used to prepare main courses such as meat dishes, which are more palatable when hot.
Commercial heat sources for self-heating food packaging use an exothermic (heat releasing) reaction between quicklime, or calcium oxide, and water. Quicklime, inexpensive and readily available, is generally recognized by the FDA as safe. The product of the reaction is calcium hydroxide.
For the US military's Meals Ready to Eat (MRE), the flameless ration heater design oxidizes magnesium metal, using iron and salt as a catalyst. Water activates the heater, and hydrogen gas is released as a byproduct. Civilian versions are available; it is possible to buy heater packets individually.
Current research focuses on cost reduction using reactions without odour or fumes. One heat source in development uses air-activation reactions that utilize oxidation of common metals like iron or zinc. Another uses solid fuel energy storage technology. The heating element contains aluminium and silica, two benign materials, which in an intimately mixed powdered state can undergo a chemical reaction to give off a large amount of heat. The small heater unit is formulated to give high utilization of the chemical energy content and generates 720 calories of heat per gram.  To view a demonstration of the aluminium/silica self-heating "Self-Heating Coffee Demonstration" on YouTube. Neither technology is commercially available.