Re: Shattered rear Window
"I thought all glass on a car had to be safety glass"
You are correct, all of the side and rear glass is tempered (which is extremely strong, but shatters into a million tiny squares when chipped), and the windshield is laminated glass (which has a PVB layer between two sheets of thin, flexible plate glass, which when broken, the PVB stretches and deforms to hold the glass shards together to hold you in, but who's glass edges are incredibly sharp so they'll cut skin if touched).
The reason why the windshield is different is because stone chips cause it to get impacts far more often.
Laminated glass is very soft. Individual stone chips don't always, immediately propagate, and when they do, overall visibility is usually still possible. Its flexibility is key to being able to laminate the layers together (the two sheets of curved glass must be able to conform to each other, and the PVB sheet, during the process to avoid air bubbles or gaps which would affect visibility).
So, although tempered glass windshields were used for some time (up until the '60s in the US, sometime later in Europe), the rule was eventually changed to laminated glass, so that at high speeds a single stone chip would not result in the whole thing in your face and lap.
Tempered glass, because it is so strong, and because stone chips and high speed are rare in bathrooms and buildings, it is the usual go-to for building construction where strength is required. Also, tempered is way cheaper to make, than laminated.
By the way, in recent years, high end vehicles have begun using laminated glass on the side windows, because the inner, resin sheet can provide a noise dampening benefit. Although the window costs more it makes the cabin quieter.
Last edited by norm356; 05-17-2019 at 10:22 AM.