Abstract: A thermal storage composition activated by exposure to microwave energy is provided. The thermal storage composition preferably comprises a mixture of at least two impregnated powders where a first powder is calcium silicate impregnated with a microwave-sensitive material, and a second powder is calcium silicate impregnated with a phase-change material to provide a free-flowing powder; the thermal storage mixture may be utilized in a container, to provide a thermal storage construction (heating construction) comprising a seat cushion having a thermal storage unit therein; further, a process of storing thermal energy for release over an extended period of time is described.