Dummies' Guide - How to Stop Your Car Windows Fogging Up

Foggy windows are more than annoying. A fogged windscreen is a safety hazard, and in wet, humid New Zealand it happens all the time. The cause is simple, and so are the fixes. This guide covers what's going on, a quick fix for the morning drive, how to stop it coming back, and what works when you sleep in your car.

Why Windows Fog Up

Warm, damp air meets cold glass and turns into tiny droplets. The damp comes from your breath, wet clothes, wet shoes, damp mats, and sometimes leaks. The more moisture inside the car, and the colder the glass, the worse it gets.

The Quick Fix for Your Morning Drive

1. Turn the fan up and point the vents at the windscreen.
2. Switch the air-con on. It dries the air, so it clears fog faster, even when you have the heater on.
3. Turn recirculation off so the car pulls in fresh outside air instead of recycling the damp cabin air.
4. Turn the temperature up. Warmer air holds more moisture.
5. Crack a window briefly to let the damp air out.
6. Wipe any remaining fog with a clean, dry microfibre cloth.

How to Stop It Coming Back

• Clean the inside of the glass. A dirty film gives water something to cling to, so clean glass fogs less.
• Get the wet things out of the car. Don't leave damp towels, wet clothes or a wet umbrella inside.
• Dry your mats if they get soaked.
• Check for leaks. A musty smell or damp carpet can point to a bad door seal or a blocked drain. That's worth fixing.
• Use the air-con regularly, even in winter, to keep the system working and the air dry.
• Anti-fog treatments exist, and results vary.

If You Sleep in Your Car

Overnight, your breath pours moisture into a closed car, and the glass can end up streaming with water by morning. Car campers who have battled this agree on the main fix: ventilation.

• Crack the windows a little, ideally on opposite sides of the car, so air flows through.
• Add a small battery-powered fan to keep the air moving.
• Ventilate in winter, too. It feels backwards when you're cold, but opening a window a little reduces the humidity that causes fog and frost inside.
• Don't rely on moisture absorbers alone. Some campers found no difference, and others found some benefit.

Safety first: never use an unvented fuel-burning heater in a car you're sleeping in. Carbon monoxide can build up and kill. Use warm layers and a good sleeping bag instead. For the full set-up, rules and fines, read our car-sleeping guide.

A Quick Checklist

1. Fan up, air-con on, recirculation off, warm air at the screen.
2. Clean the inside of the glass.
3. Remove wet items and dry the mats.
4. Check for damp carpet or a musty smell.
5. If you sleep in the car, crack two windows and add a fan.

Winter trip planned? See our winter road trip checklist.

This guide is general advice. If your air-con or demister isn't working, get it checked.

Need a Hand?

Air-con or demister not working, or a leak you can't find? Visit Our Workshop to book a service. Need a part, like a door seal? Request a Part.