Abstract: The effectiveness of heat transfer to and from a thermal energy storage medium, for example a phase change medium, is enhanced by the inclusion of thermally-conductive elements within the thermal energy storage medium. The thermally-conductive elements may be filler shapes placed in a self-supporting stacking arrangement, which may be a random stacking arrangement. The effective thermal conductivity of the matrix that includes the thermal energy storage medium and the thermally-conductive elements is higher than the thermal conductivity of the thermal energy storage medium itself. Other thermally-conductive elements may be used, for example thermally-conductive sheets.