To enter an initial jelly-like, semi-solid phase during a resin curing process.

Gel coat

An unreinforced, clear or pigmented coating resin applied to the surface of a mold or part to provide a smooth, more impervious finish on the part exterior.

Gel time

The period of time from initial mixing of liquid reactants in a resin to the point when gelation occurs as defined by a specific test method.

Glass fiber

see fiberglass.

Glass transition

A reversible change in an amorphous polymer between a viscous condition and a hard, relatively brittle condition.

Glass-transition temperature (Tg)

Approximate temperature at which increased molecular mobility results in significant changes in properties of a cured resin. The measured value of Tg can vary, depending on the test method.


Process of pyrolysis at very high temperatures (up to 2982°C/5400°F) that converts carbon to its crystalline allotropic form.

Graphite fibers

Carbon fibers that have been graphitized by heating and stretching at temperatures above 1649°C/3000°F.