What physical property of annealed glass is changed when it is tempered?

Tempering glass involves a process that exposes the glass to extreme heat followed by rapid cooling, which significantly increases its physical properties. One of the most notable changes is in the tensile or bending strength.

When glass is tempered, the process induces compressive stresses on the surface of the glass while creating tensile stresses in the interior. This makes the glass much stronger and more resilient to impacts and thermal stress compared to annealed glass. The enhancement in strength is critical in applications where safety and resistance to breaking are paramount, such as in building façades, shower doors, or glass railings.

While thermal resistance might also be improved due to the increased strength, the most pronounced and relevant property that distinguishes tempered glass from its annealed counterpart is its tensile and bending strength. Translucency and color do not change as a result of tempering; these properties are inherent to the glass material itself and remain the same regardless of whether the glass is annealed or tempered.