Made using natural minerals, sapphire glass is a single crystal aluminum oxide (Al2O3), also known as wear resistant glass. Its chemical structure is the same as crystal structure, so it is named as crystal glass as well. Sapphire glass is one of the hardest materials with Mohs hardness 9. Various colors can be generated by adding various chemical elements. Colorless is the most commonly used glass type.

Sapphire glass/ruby glass has excellent thermal properties, excellent electrical and dielectric properties, and chemical corrosion resistance. It is resistant to high temperatures, and features good heat conductivity, high hardness, infrared transmission, and good chemical stability. Therefore, the crystal glass is often used to replace optical materials to make optical components and infrared optical windows. It is widely used in infrared and far-infrared military equipment, and has widely applied in high-precision instruments for marine and aerospace.