Why Does My Windshield Fog Up When It Rains?

Understanding Condensation vs. a Real Water Leak

There’s nothing worse than hopping into your car on a rainy day and instantly watching your windshield fog up. Visibility drops, you crank the defroster, and start guessing—is this just humidity… or is there a leak somewhere?

At Hampton Auto Glass, we get this question all the time. Here’s what’s really happening and how to tell the difference between normal condensation and a true water leak inside your vehicle.

🌧 The Science Behind Foggy Windows

When it rains, the air outside cools down and becomes saturated with moisture. Inside your car, the air is often warmer—especially if you’ve been driving or have the heater on. That temperature difference causes moisture in the air to condense on the cooler glass surface of your windshield.

Think of it like a cold glass of lemonade on a summer day—the moisture you see is water vapor in the air turning back into liquid form.

Common causes of condensation include:

• Wet shoes, umbrellas, or floor mats adding humidity inside the car

• Recirculating air mode trapping moist air inside

• Temperature differences between the cabin and outside air

• Lack of air conditioning or defrosting airflow

💧 Condensation: The Harmless Kind

If your windshield fogs up but the glass stays dry to the touch, that’s condensation. It often appears as a misty film that wipes away easily.

Quick tips to clear it up:

1. Use the defrost mode — this directs warm, dry air onto the windshield.

2. Turn on your A/C — even in cold weather, your air conditioner removes moisture from the air.

3. Crack a window — a bit of ventilation helps balance humidity levels.

4. Clean the inside of your windshield — dirt and film make fogging worse.

Condensation is perfectly normal, especially on damp, rainy days.

🚿 Water Leak: The Problem Kind

If you notice actual water droplets, damp carpets, or musty smells, that’s not condensation—it’s a leak.

Common leak sources include:

• Faulty windshield seal – sometimes after a windshield replacement, a small gap or failed bond allows water to sneak in.

• Clogged sunroof drains – debris can block the drainage tubes and cause overflow into the cabin.

• Door seals or weatherstripping – cracked or worn rubber can let rain in during storms.

• HVAC drain hose issues – if your A/C condensation drain is blocked, it can back up into the cabin.

A leak can cause more than just fog—it can lead to mold, rust, or electrical damage over time.

🧰 How Hampton Auto Glass Can Help

If you suspect a leak around your windshield, bring your vehicle to Hampton Auto Glass. Our technicians can perform a leak inspection and reseal if necessary. With over 35 years of experience serving Clark County, we know exactly how to pinpoint whether that moisture is from normal weather conditions—or from a problem that needs fixing.

We’ll make sure your windshield is sealed tight, safe, and clear—rain or shine.

🚗 Stay Clear, Stay Safe

A fogged-up windshield doesn’t always mean trouble—but knowing the difference can save you time, money, and stress. Next time your windshield fogs up during a rainy drive, take a closer look: misty haze that wipes off easily? Condensation. Pooled water or soggy floor mats? Time for a professional inspection.

Hampton Auto Glass — Serving Clark County for over 35 years. Home of the $50 rock chip.Visit HamptonAutoGlass.com or stop by our West Vancouver or

East Vancouver/Camas locations for expert auto glass care.