The tempered glass that Lixit water bottles are made from is meant to be extraordinarily durable. Tempered glass starts as a annealed glass. Glass that is not annealed is less durable similar to the drinking glasses in your cupboard, and may crack or shatter under relatively small temperature changes or bumping into other objects.
When glass is annealed it’s heated to be soft enough for the stresses to relax but hard enough so it will not deform. The glass is then slowly cooled which relieves the stresses created when the glass was formed.
The tempering process takes annealing step further. The annealed glass goes into a furnace and heated above its annealing point which is usually about 720 degrees C. Then forced air cools the exterior of the glass quite rapidly while the inner part of the glass receives the cold air flow for shorter period.
Fully tempered glass is 4 to 6 times stronger than annealed glass. Tempered glass is typically used on the side and rear windows and automobiles (windshields are usually made of laminated glass which will not shatter when broken.)