Laminated glass is produced from dual layers of glass sandwiching a layer of PVB (polyvinyl butyral). This sandwich is then subjected to heat and is run through a series of rollers. The heat and pressure causes the PBV to chemically and mechanically to bond to the glass layer on either side of it.
It is the layer of PVB that gives the glass its energy absorption characteristic should the car be involved in a collision as well as resisting penetration from anything that may be flying through the air. Laminated glass will break and a hole can be punctured through it but because of the PVB layer it stays intact.
Laminated auto glass does two extremely important things; it assists in deploying the airbag properly and it keeps passengers in the car rather than being thrown through the window.
The air bag on the driver’s side of the car comes straight out from the hub of the steering wheel; the air bag on the passenger’s side however first deflects off the windshield and then encompasses the passenger. This whole thing happens in a nano-second and can develop a force of 2,000 pounds. The windshield has to be able to withstand both the high speed and the extreme force; otherwise it will not protect the passenger as intended. Due to its extremely high strength, laminated auto glass will keep the driver and the passengers inside the cars cocoon should there be a collision. In the not too distant past is was not uncommon for the occupants to be thrown through the front window.
Tempered glass is equally important to safety as is laminated glass; it differs however in form as well as function. Tempered glass is used for all windows except the front; it is made by heating a single layer of glass and then quenching it quickly and then running the glass through high pressure blowers to bring it to room temperature.
The outer surfaces cool much faster than the inner core and contracts, this contraction cause’s compression while the center, which cools much slower, causes tension. It is the manipulation of stresses that give tempered glass its strength, tempered glass is between five and ten times as strong as glass which has not gone through the tempering process.
A combination of laminated and tempered auto glass allows the car to withstand the use and abuse that a car gets day in and day out.