coefficient of expansion

Coefficient of expansion (COE) is the rate at which a material expands when heated.

For kilnformed glass artists, the COE is shorthand for describing glasses that are compatible with each other.  For example, Spectrum's System 96 glass (as well as compatible glass that is manufactured by Uroburos) is often described as simply "96 glass".  Simillarly, Bullseye's compatible glass is frequently referred to as "90 glass".

While useful as a shorthand way to describe families of compatible glass, it is important to understand that expansion rate, though critical, is not the only thing that determines compatibility between glasses.