Where Did that Windshield Crack Come From?

Yesterday, you drove home and your windshield was fine. This morning you went to start the car, and there’s a crack in the windshield. Nope, it wasn’t angry birds or the neighborhood hooligans. It was just natural science class stuff causing the glass to crack.

A windshield is a complex combination of glass, plastics, and urethane. As such, it is susceptible to the things that make glass break – stress, heat, cold, and surface erosion.


Driving anywhere the windshield is under stress from the air pressure, the vibration of the vehicle, jolts from pot holes and rough driving surfaces and the flexing of the glass as it moves with the vehicle. Over time these stresses can cause the glass to weaken. Add in any really small abrasions from surface erosion, and, magic, a crack can form in a weak area of the windshield.

Heat and Cold

Together heat and cold are powerful agents working against your windshield. During the day left in the sun, the temperature inside your vehicle is much hotter than the temperature outside. The heat causes the glass to expand. At night or parked in the shade, it’s cooler and the glass contracts to it’s normal size. Expanding and contracting are like bending a stick back and forth. Bend it enough times and eventually the stick (or windshield) will break.

Surface Erosion

Surface Erosion is the action of water, dirt, stones, and pebbles working on the surface of your windshield. Although you may not be able to see it, debris can cause little chips in the auto glass. Take those little holes and add in water from the rain. Freeze that rain (in places like Michigan) in the winter and suddenly an invisible chip turns into a crack as the ice expands breaking the glass.

If your windshield cracks, be sure to take your car, truck or SUV to a qualified professional for replacement. Using cheap glass or uncertified installers will just bring you back to the glass shop sooner than expected.