Abstract: Single-use heat transfer container has an insulated product chamber containing a reaction vessel holding two separate reactants. The product chamber is partially defined by the reaction vessel which is integrally sealed thereto near a lower end of the container. The reaction vessel has a flexible bottom that is responsive to external pressure. An activation pin on the interior of the bottom is capable of piercing a barrier inside the reagent vessel when the container bottom is depressed. The resulting mixing of the separately stable reactants in the vessel initiates the desired heat transfer reaction. The container may have a cover including storage compartments for user dispensable additives. The method of making the inventive container is disclosed.