A heat unit containing a phase change material consisting of polyethylene glycol and a fatty acid combination of stearic and palmitic acids is disclosed. When heated in a microwave for about four (4) minutes the heat unit reaches a temperature of about 70 C. (158 F.). When placed in an insulated container, the heat unit will, after six (6) hours, have a temperature of about 40 C.-55 C. (104 F.-131 F.). The heat unit is advantageous for maintaining food hot during transport as well as other uses where long term heat emission is needed.

A container assembly has a soft-sided insulated wall structure. It has an internal chamber in which to place objects, such as foodstuffs, to be kept cool or warm. There is a first closure member that opens and closes to permit objects to be place in, or removed from, the chamber. The wall structure includes one or more accommodations in which to place a warming or cooling element, such as an ice pack. The accommodations are externally accessible without opening the main chamber, and have their own closure. The outside of the accommodation may be insulated; the inside is a thin web through which to transfer heat. The container may be a collapsible foldable bag; a tote bag; back pack or a non-collapsible lunch box. The thermal storage elements may have a flat disk shape. The external access for the thermal storage elements permits them to slide sideways into place.