Toughened glass is defined in BS EN 12150-1: 2015: Glass in building – Thermally toughened soda lime silicate safety glass. In this standard, it is defined as:

‘glass within which a permanent surface compressive stress, additionally to the basic mechanical strength, has been induced by a controlled heating and cooling process in order to give it greatly increased resistance to mechanical and thermal stress and prescribed fragmentation characteristics’

For more specific details, please refer to the standard, BS EN 12150-1: 2015: Glass in building – Thermally toughened soda lime silicate safety glass. (www.bsigroup.com )