Glass transition
The liquid-glass transition (or glass transition for short) is the reversible transition in amorphous
Amorphous solid
In condensed matter physics, an amorphous or non-crystalline solid is a solid that lacks the long-range order characteristic of a crystal....

 materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle state into a molten or rubber
Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...

-like state. An amorphous solid that exhibits a glass transition is called a glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

. Supercooling a viscous liquid
Viscous liquid
In condensed matter physics and physical chemistry, the terms viscous liquid, supercooled liquid, and glassforming liquid are often used interchangeably to designate liquids that are at the same time highly viscous , supercooled, and able to form a glass.- Working points in glass processing :The...

 into the glass state is called vitrification
Vitrification is the transformation of a substance into a glass. Usually, it is achieved by rapidly cooling a liquid through the glass transition. Certain chemical reactions also result in glasses...

, from the Latin vitreum, "glass" via French
French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...


Despite the massive change in the physical properties of a material through its glass transition, the transition is not itself a phase transition
Phase transition
A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another.A phase of a thermodynamic system and the states of matter have uniform physical properties....

 of any kind; rather it is a laboratory phenomenon extending over a range of temperature and defined by one of several conventions.