Synthetic sintered mullite is a specialty in the portfolio of ceramic raw materials made by Nabaltec . In addition to the pure and stoichiometric sintered mullite with the brand name SYMULOX® M 72, Nabaltec also offers a sintered zirconia containing mullite called SYMULOX® Z 72 as well as synthetic reactive mullite named SYMULOX® M 672. There are already a number of ceramic manufacturers offering fused mullite on the worldwide market. However, there are significant differences between the fused and the synthetic sintered SYMULOX®. One of the specific features of the synthetic sintered SYMULOX® mullites is the highly homogeneous phase constitution, low amount of impurities, and a high degree of structural micro-crystallinity. The crystal size of the synthetic sintered mullite amounts to a maximum of 50 µm for SYMULOX® M 72, a maximum of 20 µm for SYMULOX® Z 72 and about 2 µm for SYMULOX® M 672, while the fused ones exhibit much larger crystal sizes, up to some centimeters. Micro-crystallinity in SYMULOX® is the reason for the good physical parameters, such as thermal shock resistance.