You walk out to your car on a cold Denver morning and notice a crack running across your windshield that was not there yesterday. No rock hit your car. No visible impact point. What happened? You are likely looking at a stress crack, and understanding how it differs from an impact chip is important because the two require very different approaches.
What Is an Impact Chip?
An impact chip is caused by a physical object striking the windshield. There is always a visible impact point -- a small divot, cone, or crater in the glass where the object made contact. The damage radiates outward from that central point in patterns like bulls-eyes, star breaks, or combination breaks. Impact chips are the most common type of windshield damage in Denver, caused by road debris, gravel, and construction materials.
What Is a Stress Crack?
A stress crack appears without any impact. It is a clean, linear crack that typically starts at the edge of the windshield and extends inward. There is no chip, no divot, and no visible impact point. The crack seems to appear out of nowhere, usually overnight or after a rapid temperature change.
Stress cracks are caused by structural stress on the glass itself, not by an external object. In Denver, the most common causes are:
- Rapid temperature changes: Pouring hot water on a frozen windshield, blasting the defroster on full heat against ice-cold glass, or the natural 40-degree temperature swings Denver sees regularly
- Installation defects: A windshield that was installed with uneven pressure on the seal can develop stress points that eventually crack
- Structural flex: Driving over Denver's severe potholes -- especially on roads damaged by winter freeze-thaw cycles -- can flex the vehicle frame enough to stress the windshield
- Pre-existing micro-damage: A tiny edge chip or nick that you never noticed can serve as a starting point for a stress crack when thermal or mechanical stress is applied
How to Tell Them Apart
| Feature | Impact Chip | Stress Crack |
|---|---|---|
| Impact point | Visible divot or crater | No impact point |
| Starting location | Anywhere on the glass | Usually starts at the edge |
| Pattern | Circular, star, or branching | Single clean line |
| Cause | Object hit the glass | Temperature or structural stress |
| Repairable? | Usually yes (if small) | Rarely -- usually needs replacement |
Why Stress Cracks Usually Cannot Be Repaired
Stress cracks present several challenges that make repair impractical in most cases. First, they typically start at the windshield edge, which means the structural seal between the glass and the vehicle frame is already compromised. Second, stress cracks tend to be long -- they often extend 6 inches or more by the time you notice them. Third, without an impact point to anchor the repair bridge, the resin injection process is less effective.
Most importantly, the underlying stress that caused the crack in the first place has not been resolved. Even if resin could fill the crack, the ongoing thermal or structural stress would simply cause a new crack to form next to the repair. For this reason, stress cracks almost always require a full windshield replacement.
Impact Chips Are Almost Always Repairable
The good news is that impact chips -- the far more common type of damage in Denver -- are almost always repairable when caught early. The impact point provides a natural injection site for the repair resin, and the damage pattern is self-contained rather than driven by ongoing stress. If your chip is smaller than a quarter and has not developed cracks longer than 6 inches, professional repair will restore your windshield's integrity and prevent further spreading. Read our detailed guide on when chips can be repaired.
Insurance Differences in Colorado
Insurance treatment can differ between stress cracks and impact chips. Impact chips are clearly covered under comprehensive glass coverage because they result from an external event (road debris). Stress cracks can sometimes be disputed by insurers who argue they resulted from a pre-existing condition, installation defect, or owner action (like pouring hot water on frozen glass). However, most Colorado insurers cover stress cracks under comprehensive as well, since they result from environmental conditions rather than driver fault. Check our insurance guide for details on Colorado coverage.
Preventing Stress Cracks in Denver
While you cannot control Denver's temperature swings, you can reduce your risk of stress cracks:
- Never pour hot or warm water on a frozen windshield -- use a proper ice scraper
- Warm your defroster gradually rather than blasting it on the highest setting against ice-cold glass
- Park in a garage or use a windshield cover during extreme cold snaps
- Repair any edge chips immediately, as they serve as initiation points for stress cracks
- Avoid slamming doors hard, which can flex the frame and stress the glass