Tumbler

The tempering process is what makes Duralex so tough. Glass that has been heated to around 700°C is suddenly cooled by cold air ventilation.
This treatment creates controlled stress in the glass which improves most of its physical qualities: resistance of mechanical stress (bending, impacts) and thermal shock.
Duralex glass is 2.5 times stronger than annealed glass and resistant to a thermal shock of 130°C. This also applies to tempered glass that is used to make windscreens.
Upon impact or accident, they burst into thousands of blunt pieces.