By the nature of the toughening process it is not possible to produce toughened glass as flat as annealed glass. Two types of deviation, known as overall bow and roller wave, can be produced.

Overall bow may vary dependent upon the glass type/ thickness, size, aspect ratio and other factors. Roller wave is caused by the glass moving across rollers at high temperatures. This will give a very slight waviness which varies with glass thickness and pitch of rollers.

Standards such as BS EN 12150-1 for toughened soda lime silicate safety glass state acceptable limits of overall bow and roller wave.  For more details of processing capability, the toughened glass supplier should be consulted.

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