Heat strengthened glass is a heat treated glass that goes through a similar process to that for toughened glass, resulting in glass that is
typically 1.5 to 2 times stronger than annealed glass, but not as strong as toughened glass.  It breaks in a similar manner to annealed glass, so would not normally be classified as a safety glass.  It is increasingly used in laminated glass, i.e. to produce laminated heat strengthened glass.

Heat strengthened glass is defined in accordance with BS EN 1863-1 and should be CE Marked to BS EN 1863-2.