If a hard object impacts a car window, the glass typically shatters into small pieces. However, if your windshield receives a hard impact, it leaves the surface cracked. Why is this the case?
Finding the right type of material for the windshield initially took a little trial and error. When vehicles were first manufactured, they were created with plate glass. This proved to be extremely dangerous because once an accident occurred, sharp glass shards flew everywhere. During an accident, the glass was nearly just as dangerous as the impact of the crash.
In the late 1920s, automakers began searching for an alternative and eventually stumbled upon an innovative option. Édouard Bénédictus, a French chemist and artist, patented a laminated glass that is reported he discovered by mistake. While he was in a lab, he dropped a flask holding plastic. The plastic inside the flask created a film that allowed the glass to break, but not shatter. By 1927, car manufacturers started incorporating the laminated glass into windshields.
Side windows aren’t installed with laminated glass; they are installed with tempered glass. Tempered glass is created by being rapidly heated and cooled, making the glass over 5x’s more durable. This explains why when it’s broken, the glass shatters into pebble-like pieces. Tempered glass for the side windows is easier to break for emergencies.