⁑As per an independent report about the Fischer HeatCore:
“A chamotte brick is essentially composed of the oxide components silicon dioxide and aluminium oxide. Chamotte bricks are classified according to their aluminium oxide content. With an outstanding thermal conductivity of 1.4 W/m*K, heat is conducted highly effectively through the brick; it is this characteristic, in combination with their specific heat capacity of 1.00 kJ/kg*K that makes chamotte bricks an excellent raw material for heat storage units. Depending on the initial materials used and the manufacturing processes employed, a range of different bulk densities can be achieved with chamotte bricks.