Windshield technology has improved considerably in recent years. Plain, flat window glass in the early cars left the place for tempered glass, which broke into pieces when it broke, but not the sharp parts. As early as 1919, Henry Ford began experimenting with laminated glass – two panels intercalating a layer of cellulose. The glass could break but not break into pieces. The father of American automobile manufacturing ordered the use of laminated glass in all Ford cars by 1929. The first were flat rolled windscreens. Modern windshields are curved. Modern laminated windshields also use polyvinyl butyrate as the filler between the two pieces of glass. It is the safest windshield glass to go.
It is not uncommon for small stones to be thrown up on your windshield while you drive. You may not notice the tiny chips that spoil the surface of the windshield – until temperatures drop below freezing outside and a barely visible chip develops suddenly in a crack. You can aggravate the situation by thawing your windshield by pouring hot water over it.
The problem is caused by the car’s metal structure expanding and contracting (due to extreme temperatures) at a different speed than the windshield glass. This causes additional stress on the cold glass, especially at the pointed ends of a crack, resulting in the serous risk of further separation.