Heat strengthening is a process applied to regular annealed float glass. It involves a furnace processing similar to tempered glass but does not meet the standards of Grade A safety glass. The strength of heat-strengthened glass is approximately twice that of regular annealed glass, while tempered glass is about five times stronger than regular annealed glass, and falls under Grade A safety glass. When heat-strengthened glass breaks, it shatters into large chunks rather than small pieces like tempered glass. Upon breakage, its appearance is similar to regular glass, but the fragments remain interconnected and within the frame. Heat-strengthened glass exhibits good resistance to thermal stress, albeit lower than tempered glass.