In the 75 years we’ve been in business repairing and replacing auto glass, one question we get frequently, especially in hotter weather is – can heat crack a windshield? If so, at what temperature does glass break? How safe is your car?
The answer to this question is more complex. While heat can indeed crack a windshield, it’s not the only factor that comes into play. The type and quality of glass used in your windshield, sudden temperature changes, and any existing damage or flaws can also contribute to a windshield cracking under high temperatures.
Let’s look closer at how heat affects auto glass and what you can do to prevent your windshield from cracking.
How Does Heat Affect Auto Glass?
Heat makes glass expand, and if the expansion rate becomes too high, it can cause cracks or even shattering. However, glass varies greatly in its resistance to temperature changes. Still, all glass types respond the same to heat, with the only difference being the rate at which they can expand and withstand pressure.
Some glass types are much stronger and more resistant to heat compared to others. For example, there are two types of auto glass, and both can withstand more heat and pressure than regular glass.
The side and back windows of most cars are made with tempered glass. The auto glass industry makes this safety glass by heating glass to 700°C and then rapidly cooling it.
This process makes the glass very strong and causes it to shatter into small, rounded pieces instead of sharp shards when broken. Moreover, tempered glass can withstand 2.333 times more heat than regular glass before it starts cracking.
But did you know that tempered glass alone isn’t enough to make windshields like it makes car side and back windows? Instead, auto glass makers use laminated glass to make windshields.
Laminated glass has two tempered glass layers sandwiching a polyvinyl butyral (PVB) layer. In case of impact or heat enough to shatter the tempered glass, this plastic layer helps hold the broken pieces together and prevents the windshield from shattering.
So, laminated glass makes it safer for the driver and passengers during accidents. While its design helps it withstand high temperatures better than tempered and regular glass, it’s not entirely immune to heat-related issues.
When exposed to extreme heat, the plastic layer between the two pieces of glass can expand and contract at a different rate than the glass itself. Those uneven expansions and contractions stress the glass, making it more susceptible to cracking.
So, Can Heat Crack a Windshield?
Yes, heat can absolutely cause a windshield to crack. In fact, extreme temperatures are one of the most common causes of windshield cracks.
There are a few factors that can contribute to this vulnerability:
1. Direct Sunlight
Parking your automobile in direct sunlight for many hours causes your auto interior temperature to rise dramatically. This increase in temperature puts added stress on the windshield, making it more likely to crack.
2. Temperature Fluctuations
Extreme temperature fluctuations, from hot to cold or vice versa, can also cause a windshield to crack. The varying rates at which the glass and plastic layers expand and contract can put too much pressure on the windshield, resulting in a crack.
3. Existing Damage
If your windshield already has chips or cracks, heat can exacerbate these issues and cause them to spread. The heat weakens the structural integrity of the glass, making it more prone to further damage.
So, you should know when to replace your windshield.
At What Temperature Does Glass Break?
The exact temperature at which glass will break varies depending on the type of glass and its thickness. It also depends on the rate at which the temperature changes and the structural integrity of the glass itself.
Generally, thin, regular glass starts to crack when heated at about 302°F (150°C). Tempered glass can either be annealed or heat-treated. According to AIS Glass, “Annealed tempered glass withstands up to 428°F (220 °C), while heat-treated tempered glass can withstand up to 662°F (350 °C).”
Remember, regular or tempered glass with chips or cracks may succumb to heat earlier than our stated thresholds. But what if the tempered glass is in perfect condition, and then you use two layers and reinforce them with a PVB layer?
Isn’t that how you make laminated glass for windshields? That’s why windshields are better adapted to withstand higher heat than side and back car windows. Additionally, the PVB layer provides more structural strength, preventing the windshield from shattering into small pieces.
Imagine a long, hot summer and an unbearable heatwave suddenly hits your town. You park your car in the scorching sun and return after a few hours. You may find your windshield cracked and other car windows shattered.
If that ever happens to you, find out: “Does Auto Insurance Cover Glass Repair and Replacement in Kentucky?”
Can a Car Window Shatter from Heat?
Yes, a car window can shatter from heat, but that’s rare. As stated earlier, the type of glass and its thickness play a significant role in determining when it will break. Also, car windows are not exposed to direct sunlight for long periods like windshields, so the chances of them shattering from heat are much lower.
As we noted earlier, car windshields are built differently from other auto glass. It’s easier to shatter tempered glass by exceeding its temperature tolerance. However, the plastic layer in windshields provides an additional barrier and makes it more resistant to extreme temperatures.
Also, car windows are typically much smaller than windshields, so the heat is not evenly distributed across the glass surface. Thus, the chances of a car window cracking from heat are lower than windshields.
However, in scorching weather, windscreens and auto glass may crack. But windscreens are structurally more shatter-resistant than car windows, which are not reinforced with plastic layers.
Furthermore, if you live in a dry climate or an area prone to heatwaves, it’s essential to keep your car parked in a shaded area and invest in sunshades for your windshield. These simple measures can help protect your auto glass from extreme heat and prevent potential damage.
Final Thoughts on Auto Glass and Heat Exposure
The effects of heat on car windows vary depending on several factors, like the type of glass and its thickness, duration of exposure, and presence of protective layers. While car windows are less likely to shatter from heat than windshields, it’s still essential to take precautionary measures to protect your auto glass from extreme weather conditions.
Always fix or replace any damaged auto glass as soon as possible to ensure the safety of yourself and others on the road. Contact Right-Way Auto Glass to fix your cracked car window or windshield right away in Louisville, Lexington, London, Morehead, and surrounding areas in Kentucky.
