How to Reduce Condensation Inside Your Car

To reduce condensation inside your car, cut the amount of water the cabin holds. Remove wet coats, umbrellas and mats when you get out, dry the interior with the air-con and heater before parking, keep the inside of the glass clean, and leave moisture absorbers in the car overnight. Condensation forms when warm, humid air touches cold glass, so less moisture in the air means less water on the windows by morning. If heavy condensation keeps appearing despite good habits, look for a leak.

Why does condensation form inside a parked car?

The Met Office explains that water vapour condenses into droplets when a surface cools to the dew point, the temperature at which condensation begins. Overnight, glass and the car roof cool quickly, and the humid air trapped in the cabin condenses on the coldest surfaces first: the windscreen, side windows and metal pillars.

Every source of moisture adds to that water: your breath during the journey, rain on clothes, wet shoes, a damp dog, snow melting off boots. The RAC puts frozen and fogged glass down to high humidity in the vehicle mixed with a cold surface. You cannot change the weather, but you can control how much water is shut inside.

Which daily habits make the biggest difference?

• Empty the car of wet things. The RAC advises removing wet clothing, shoes and towels promptly. A soaked coat on the back seat can put a surprising amount of water into the air overnight.
• Knock snow and rain off before getting in. Stamp boots and shake umbrellas outside the door.
• Bring wet mats indoors. Carpet mats hold water for days in a closed car. Rubber mats can be tipped out and wiped.
• Avoid eating takeaway or drinking hot drinks in a stationary car with the windows shut on a cold evening, as the steam ends up on the glass.
• Crack a window when it is safe on dry days to let the cabin air exchange with the outside.

How should you use the heater and air-con before you park?

The RAC describes the air-con as working like a dehumidifier, because the air coming out of the vents is dry, and recommends running it regularly throughout the year, including winter. Use that to your advantage at the end of each trip:

1. For the last few minutes of the journey, set the heater warm with the air-con on and fresh air selected, not recirculation.
2. Direct the airflow at the screen and footwells.
3. On arrival, open the doors for a moment to let the warm, damp air escape before locking up.

That leaves drier air in the cabin as it cools, so less of it ends up on the glass.

Do moisture absorbers and dehumidifier bags work?

They help, especially in cars that sit for days at a time. The RAC suggests silica gel products left in cup holders and side pockets. Reusable dehumidifier bags filled with silica can be dried out on a radiator or in a microwave, following the maker's instructions, when the indicator changes colour.

Set realistic expectations. A bag or two will soak up the everyday humidity in a dry car. It will not keep up with a footwell full of water, so if the bag saturates within days, treat that as a warning sign rather than a reason to buy more bags.

Does a clean interior really reduce condensation?

Yes, in two ways. Clean glass gives droplets less to cling to, so the windows clear faster and you are less tempted to set off with a smeared screen. And fabrics that are full of dust, food crumbs and spilled drinks hold moisture and odour. The RAC recommends wiping the inside of the windows regularly so there is no residue on the glass.

Before winter, a thorough interior clean dries out the cabin and removes the grime that holds damp. Our full interior and exterior valet, from £80, includes the inside of every window, and we work on your driveway with our own water and power. For quick fixes on the move, see our guide on clearing misted windows while you drive.

When is condensation a sign of a bigger problem?

Some condensation on a cold morning is normal. These signs are not:

• windows streaming with water even after a dry day;
• damp carpets or a wet patch you cannot explain;
• a musty smell that will not shift;
• white or green spots on seats or belts.

These point to water getting in through a seal or drain, or to mould already growing. Our guide on finding and fixing a leak into the cabin covers the checks, and where mould has taken hold, our car mould treatment starts from £80.

Sources

• RAC: How to stop your car windscreen freezing on the inside
• RAC: Should you use your air-con in the winter?
• Met Office: Dew