Manufactured from a high alumina mullite / cordierite blend. The high temperature resistance of mullite and low expansion of cordierite produces a smooth, durable surface with excellent shock resistance and long service life.  Capable of withstanding temperatures up to 1350?

Although the manufacturer states these shelves will fire to a higher temperature,

We do not recommend the 13mm shelves be fired above 1220°C. Under careful oxidising conditions, the heavier 19mm shelves will withstand temperatures of 1300°C.

                 We would warn against using these shelves in heavy reduction atmospheres.