Can cold weather crack your car windows or windshield?
As with any material, glass is subject to stress through expansion, and compression or contraction with changes in temperature. If the windshield or rear windows are completely covered in ice, then it is possible for them to crack when heating them either with the vehicle's main heater, or using the electric defrost mode. This also applies to the side windows, but, more commonly, it affects the rear window or windshield due to the direct application of heat. In fact cracking is also possible if the temperature that the glass is exposed to goes through extremes, even without being coated with ice.
Automotive windows are made using tempered glass for the side and rear window, and laminated glass for the windshield. The tempered glass is a single pane which is designed through a process which repeatedly heats and cools the glass during its production and gives it strength to withstand the normal forces that are exerted while driving. The windows are subject to flex as the body is bouncing down the road and shifting when the vehicle goes through turns. This strong glass is designed to shatter into small pieces in the event of an impact. As i mentioned before, it is under tension, but very sturdy while at the same time susceptible to shatter under the right conditions.
Pressure over a large area generally will be deflected by the glass and it will not shatter. However, a fine point of energy applied will generally cause the window to shatter into thousands of pieces. That being the case, it's possible for temperature and stress to contribute to the window shattering. In fact, this is most common on rear glass panels in vans and large SUV’s. I have seen cases of these windows actually exploding when cold or frozen and the rear electric heater element is turned on. The rapid heating of the window combined with the stress or flex of the body can cause it to shatter violently in some cases.
When it comes to windshields, they are laminated. This means that two pieces of glass are bonded together with a plastic layer in between. This strengthens the glass and while it does not make it crack proof, it is by design basically shatter proof. The windshield can be cracked slightly or appear to be shattered but because of the lamination, it will remain in one piece. This is for driver and occupant safety.
Whether it’s for a windshield or a window, you should never attempt to de-ice or defrost with hot water, as the sudden heat stress can cause window cracking.
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