Self-heating cans work through an exothermic chemical reaction between two chemicals. Popular combinations are aluminum and silica, calcium oxide and water, and copper sulfate and zinc. When the two substances combine, the reaction produces enough heat to raise the temperature of the can.
The two component chemicals are released by pressing a button on the bottom of the can. This mechanism prevents the two reactants from mixing before the consumer intends to heat the can. The primary advantage of a self-heating can is that it makes hot food and drinks available without access to a microwave, stove or other heating apparatus.
The disadvantages of self-heating cans are expense, size and uneven heating. Because space must be dedicated for the chemical reaction, self-heating cans must be larger and bulkier to hold the same amount of liquid as a traditional can. The additional packaging and chemical costs also make self-heating cans more expensive than other cans.
Self-heating cans are based on the same technology used in meals eaten by the US military and hand warmers. These cans are used for coffee, tea, cocoa and soup and were brought to market in Asia and Europe before being used in North America. Calcium oxide and water is the formula used in the original self-heating cans in the United States.