A Mullite sagger also referred to as a mullite crucible, or Saggar, is a form of ceramic container that is used in applications that require high temperatures. Mullite is renowned for its superior thermal shock resistance as well as its high temperature stability.

Mullite saggars can be found in various industries, including ceramics, metallurgy, as well as powder processing. They are constructed to resist extreme temperatures and create an environment that protects materials during heat or firing treatment processes.

They have a good thermal stability and are able to endure temperatures as high as 1700degC (3092degF) or more. They have very low thermal expansion coefficients which means they are resistant to breaking or cracking during rapid temperature fluctuations. Mullite saggars also have good chemical resistance, which makes them ideal for applications that involve atmospheric or corrosive substances.