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Heat Stregthened Glass

breakage pattern


  • Like thermally toughened glass, heat-strengthened glass is treated using a method of controlled heating and cooling which locks the surface of the glass in a state of compression
  • This method produces a glass with a bending resistance greater than that of annealed glass but less than that of thermally toughened glass since the glass is cooled more slowly. Heat-strengthened glass does not require heat soaking
  • Virtually all types of glasses may be heatstrengthened: clear and coloured Planibel, Stopsol, Sunergy, Imagin and so on
  • Some types of glasses with magnetron coatings are also available in a heat-strengthened version; this requires a few adjustments to the thermal-toughening processes
  • Heat-strengthening can be combined with silk-screen printing or enamelling
  • Use: single glazing, insulating glazing, laminated glazing and so on – primarily for applications where:
    • the risk of the glass breaking due to thermal shock (particularly with solar control glasses or those with a higher level of energy absorption) is too high
    • the resistance of the glass to breakage by bending of a maximum of 70 N/mm² is considered sufficient
  • Once treated, heat-strengthened glasses cannot be sawn, cut, drilled or processed
  • Heat strengthened glass complies with standard EN 1863


  • Spontaneous breaking

    Heat-strengthened glasses do not suffer spontaneous breakage due to nickel sulphide inclusions. Heat-strengthened glasses do not need to be heat-soaked in advance.

  • Optical performance
    • Optical distortion

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

      - overall bend of 3 mm/m*

      - localised bend of 0.3 mm/300 mm*

      * values for heat-strengthened glass using the horizontal process

    • Interference

      Heat-strengthened glasses cause interference in the same way as 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