Tempered glass  is a type of  safety glass. It is processed by controlled thermal or  chemical   treatments to  increase  its strength compared  with normal  glass. Tempering puts the outer surfaces into conpression and the inner surfaces into tension. Such stresses  cause  the  glass,   when  broken,   to  crumble  into  small granular chunks, The granular chunks are less likely to cause injury. As  a  result  of  its  safety  and  strength,  it  has  a  high  ability  of pressure resistance, heat-resistance,and shock resistance.
Toughened glass can be made from annealed glass via a thermal tempering process. The glass is placed onto a roller table, taking it through a  furnace   that   heats   it   well  above   its   transition temperature. The glass is then rapidly cooled with forced air drafts while the inner portion remains free to flow for a short time. During the cooling process, the surface is faster in cooling and solidifying than inner side of the glass,and when the inner side continues its cooling  shrinkage,  the  tension  stress  comes  up  to  increase  the strength and heat-resistance of the glass.