Tempered glass gives greater resistance against impact and is generally considered to be 5 or 6 times stronger than annealed glass of a similar thickness. When broken it shatters into small, blunt pieces, which are less harmful than those caused by normal glass breakage. However following breakage the glass no longer offers any barrier or protection as the shattered pieces crumble easily under light pressure. Commonly referred to as Toughened glass it will therefore provide protection giving safe breakage and will allow increased loading given its superior strength.

It is produced by taking normal annealed glass and submitting it to a thermal treatment during which it is heated to around 650°C and then very quickly cooled down . As a result of this treatment the glass surface is under compression, considerably increasing its resistance to bending. Therefore under the same pressures, tempered glass allows the use of thinner panes than with normal annealed glass. The tempering process also increases the resistance of the glass against thermal shock. When an impact of a certain magnitude penetrates the compressed surface of the tempered glass, the tension is released and the glass, shatters into many small harmless pieces.