Hand warmers are used in cold weather to quickly provide warmth. Many commercial hand warmers consist of a plastic package containing a solid and an inner pouch filled with water. When the pack is squeezed or activated, the solid dissolves in the water and releases heat. These solids must release a large amount of heat upon dissolving and also be safe, inexpensive, and nontoxic. The exact amount of energy released by these solids upon dissolving, known as their heat of solution, can be measured through calorimetry.