This is the base synthetic mullite. It is composed of almost 100% mullite crystals (theoretical composition) with minimal corundum crystals and glass, and has a dense structure.
Compared to aluminite, it has high hot strength, low thermal expansion and thermal conductivity, and because the primary particles grow into needle-like shapes, the material itself has high thermal shock resistance.

In terms of chemical composition, it has a higher purity and a denser structure than synthetic mullite. It has less glass phase and less loss of heat resistance due to impurities, making it less susceptible to thermal creep at high temperatures.
It also has a high degree of whiteness and is less likely to turn yellowish-brown due to Fe₂O₃ and TiO₂ when reheated, which is why it is also used in saggers and other items.

It has a higher alumina content than other synthetic mullites, giving it a high specific gravity. To further increase corrosion resistance, and minimize glass, it structured approx. 10% corundum crystals and remines 90% mullite crystals. This means that less glass is produced when it comes into contact with various impurities, and the Al concentration of the glass, as well as its viscosity and melting point, increase, resulting in a product with high heat resistance and corrosion resistance.