Heat Strengthened glass is produced by a process similar to that used for toughened glass, but the cooling process is slower. The strength developed is about half that of toughened glass and distortion is generally less. The product has many uses, but it does not meet the criteria for safety glazing because its breakage pattern resembles that of an annealed glass.

Like the toughening process, Heat Strengthening imposes limits on the maximum glass sizes.

Wired glass, some patterned / figure rolled glass cannot be Heat Strengthened.