For service temperatures up to 1300°C, the most popular type of refractory material is based upon the mineral Cordierite, a magnesium silicate with a very low coefficient of thermal expansion rendering it highly resistant to thermal shock. Most commercial cordierites are formulated to produce approximately 50% of cordierite, the remainder comprising mullite and amorphous material.

Molochite, the standard calcined clay component in these formulations contains no crystalline silica and thus imparts a low and even thermal expansion and excellent dimensional stability at service temperatures, leading to extended product life time.