Abstract: A packaged heat generator is used for warming or heating the human body, canned foods and similar objects. It consists of three bags: a first bag contains a composition of metallic powders; a second bag has a vent portion through which air is introduced, and contains the first bag and a composition of oxidation promotors in an isolated relation, such as by two-folding it, before the first use; and a third bag encloses the first and second bags, whereby for use, relatively gentle forces applied to the first and second bags with the third bag completely removed cause the two compositions to be mixed inside the second bag so that the mixtures can provide heat of oxidation and heat of hydration by exposure to air through the second bag.