Thermally strengthened glass is produced in a similar way to thermally toughened glass, but it cools at a slower rate and its strength is about half that of thermally toughened glass and is not considered to be safety glass in use. Thermally strengthened glass has undergone additional heat treatment to increase its mechanical strength. In the event of breakage, the fragments are of medium size. Thermally reinforced glass is produced up to a maximum thickness of 12 mm.

According to the harmonised European standards, monolithic thermally reinforced glass is not classified as safety glass, but as a combination element.