Macor is a machineable glass-ceramic developed and sold by Corning Incorporated It is a white material that looks somewhat like porcelain. Macor has excellent thermal characteristics, acting as efficient insulation, and stable up to temperatures of 1000 °C, with very little thermal expansion or outgassing. It can be machined into any desired shape using standard metalworking bits and tools. This combination of machinability and good thermal properties have made it the material of choice in many engineering contexts.


Macor is made up of fluorphlogopite mica in a borosilicate glass matrix. Its composition is roughly:


Macor has a density of 2.52 g/cm3, and a thermal conductivity of 1.46 W/(m·K). Its low-temperature (25 to 300 °C) thermal expansion is 93×10-7</sub> m/(m·K).

Macor is a very good insulator with excellent tolerance. Even with temperature changes, its low thermal expansion ensures that its shape changes very little.


There are no major safety concerns or toxic effects associated with Macor. Its excellent temperature stability makes it safe in most situations. The dust created when machining it can be an irritant and inhalation should of course be avoided.

Macor can burn/explode in oxygen under extremely high temperatures, or very rapid temperature changes. The flame is usually quite bright (risk of blinding), but usually extinguishes rapidly.


Macor is used in a wide variety of industries, including aerospace, nuclear engineering, medicine, and fundamental research. It is often used in high-temperature and/or high-vacuum environments, where dimensional stability and low outgassing are critical.

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