Flat glass reheated and cooled to create more surface compression than annealed glass but less than fully tempered glass.
GlassRenu · Educational illustration
Meaning and boundaries
Heat-strengthened glass is not the same as fully tempered glass and ordinarily is not safety glazing solely because it is heat-strengthened.
Why it matters in glass restoration
Its strength, breakage pattern, stress state, and restoration risk differ from both annealed and fully tempered glass.