U.S. patent application 20170188754 (inventor Melissa Zimberg, Maplewood, N.J.):
"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."