TProduced in a similar way to toughened glass, heat strengthened glass is subjected to a slower rate of cooling and therefore is only around twice as strong as annealed glass (or half as strong as toughened glass). If it breaks, it exhibits similar behavior to annealed glass. It cannot be used as safety glass on its own but, thanks to good residual strength after cracking, it does lend itself to use in a laminated pane. Heat strengthened glass does not require heat soaking.

Both toughened glass and heat-strengthened glass are resistant to large and variable changes in temperature, suiting them to spandrel panels where there is a risk of thermal cracking. They also offer good wind pressure resistance o n tall buildings and, in particular, corners.

The heating and cooling cycle required to produce toughened or heat-strengthened glass causes optical distortion in the surface. When annealed glass is heated again, it sags slightly between the rollers carrying the glass through the furnace; the subsequent cooling results in ripples, or ‘roller wave distortion’.