With drawn glass, the glass mass is drawn as a sheet directly from an opening in the furnace.
The use of a wide groove (the “debiteuse”) creates a broad sheet of glass. This sheet is immediately, and carefully, cooled down using cooler bars, so that the glass retains its shape. Afterwards it is cooled down further in a complex process that ensures the temperature diminishes gradually and in a controlled manner.
When glass cools down too quickly, it may crystallize or tear.