Front windscreen for automobiles are generally made of laminated safety glass, a type of treated glass, which consists of two (typically) curved sheets of glass with a PVB (Polyvinyl Butytal) laminated between them for safety, and are bonded into the window frame.

In the case of breakage, the glass is held in place by the interlayer PVB, retaining emergency visibility for the driver. Laminated glazing is now also increasingly being specified for car side windows. Usually the glass plies are shaped (curved) as matched pairs through heating to a temperature of around 620°C. As with tempering, the shape can be achieved through gravity 'sagging' or through press-bending for the more complex shapes. Differential heating to control temperature across the surface of the glass, and hence the resultant degree of bending, is also used for more complex shapes. The shaped glass pairs are then gradually cooled to room temperature before the PVB laminate is sandwiched between them. At this point the PVB is opaque and only becomes transparent at completion of the lamination process. This involves the removal of any air trapped in the glass sandwich through a mechanical or vacuum squeezing process, followed by the heating of the windscreen to 140°C within an autoclave, under a pressure of 10 to 15 kg/cm2, to complete the bonding of the two glass plies.

Source: Fuyao Glass Group Laboratory

Laminated glass ball drop test		Tempered glass ball drop test