Laminated Glass

Laminated glass is a type of safety glass that holds together when shattered. In the event of breakage, it is held in place by an interlayer of PVB between its two or more layers of glass. The interlayer keeps the layers of glass bonded even when broken, and its high strength prevents the glass from breaking up into large sharp pieces. This produces a characteristic "spiderweb" cracking pattern when the impact is not enough to completely pierce the glass.

Laminated glass is normally used when there is a possibility of human impact or where the glass could fall if shattered. Shopfront glazing and windshields are typically laminated glasses. The PVB interlayer also gives the glass a much higher sound insulation rating, due to the damping effect, and also blocks 99% of transmitted UV light.

Today, laminated glass is produced by bonding two or more layers of ordinary annealed glass together with a plastic interlayer, usually polyvinyl butyral (PVB). The PVB is sandwiched by the glass which is passed through rollers to expel any air pockets and form the initial bond then heated to around 70 C in a pressurized oil bath. The tint at the top of some car windshields is in the PVB.

A typical laminated makeup would be 3 mm glass / 0.38 mm interlayer / 3 mm glass. This gives a final product that would be referred to as 6.38 laminated glass.

Multiple laminates and thicker glass increases the strength. Bulletproof glass panels, made up of thick glass often toughened and several interlayers often thicker than that in windshields, can be as thick as 50 mm. A similar glass is often used in airliners on the front windows, often three sheets of 6mm toughened with thick PVB between them.