Heat-treated or tempered glass fabric is made from standard woven glass fibers and undergoes an additional finishing phase in which the fabric is passed through a high-temperature oven. This process burns off the small amounts of weaving oils and lubricants (size) present on standard glass fiber yarns. It can also help remove surface fibers, which may reduce irritation during handling.

This process results in the light brown or "caramel-colored" appearance of the fabric. Caramelized glass fabric is often specified when no fumes or "outgassing" can occur during the initial heat cycle of the end product or in applications where weaving oils and lubricants might affect adhesion to other products.