Heat Strengthened
Like toughened glass
heat strengthened is heat treated but not to the same extent. The result is a glass that is resistant to thermal shock, is flatter than normal toughened glass, but is not a safety glass. When heat strengthened glass is broken it breaks into a small number of large pieces; similar to annealed glass.
Heat-strengthened glass does not require heat soaking.The relevant standard for heat strengthened glass is BS EN 1863.