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Thermally Toughened Glass

breakage pattern


  • Glass which has been heat-treated using a method of controlled heating and cooling which locks the surface of the glass in a state of compression
  • Virtually all glasses can be thermally toughened: clear and coloured Planibel, Stopsol, Sunergy, Imagin, etc.
  • Certain types of glasses with a magnetron coating are also toughenable; this requires some adjustments to the toughening procedures
  • Thermal toughening can be combined with silk-screen printing or enamelling
  • Use: single glazing, insulating glazing, laminated glazing and so on for applications where the following are required:
    • Greater resistance to mechanical shocks (glass doors, glass units with punctual settings, etc.)
    • Greater resistance to thermal stresses (glasses exposed to solar radiation with possible shadows which cause stresses in the glass, etc.)
    • Greater protection against the glass breaking thereby reducing the risk of injury
  • Once toughened, the glasses cannot be sawn, cut, drilled or processed
  • Complies with standard EN 12150


  • Spontaneous breaking

    Toughened glass can break spontaneously due to the presence of nickel sufide. To avoid this, a Heat Soak treatment can be requested.

  • Optical performance

    The thermal toughening process causes the surface of the glass to distort in two ways:

    - Overall bend of 3 mm/m*

    - Localised bend of 0.5 mm/300 mm*

    * Values for Planibel heat-strengthened glass using the horizontal process

    This phenomenon may be more visible in coated glasses.

  • Anisotropy

    Anisotropy is caused by compression of the surface of the thermally toughened glass. Under natural lighting conditions, the reflection characteristics vary from one point to another and differently coloured patterns known as "leopard spots" may be seen on the glass.

    This particular aspect is inherent to thermally toughened glass.


Glasses may be heat-treated to enhance their resistance to mechanical and thermal shocks.


Heat Strengthend Glass

Thermally Toughened Glass

Thermally Toughened HST Glass

Tempered glass table