How to Stop Condensation in Your Car or Van Overnight
Condensation forms when warm, damp air inside your vehicle meets glass that is colder than the air's dew point, so the water vapour turns to droplets. To cut it down, let moisture out with a little ventilation all night, bring less moisture in, and keep warm cabin air off the cold glass. Thermal blinds help with that last part.
Key facts
- The dew point is the temperature at which air becomes saturated and water vapour condenses, so any surface colder than that gets wet[1][2].
- On clear, calm nights surfaces lose heat to the sky, which is why dew and frost form then, and why the glass is usually the coldest thing in a parked vehicle[3].
- Before you set off you must be able to see out of every window: clear the snow and ice, and demist them (Highway Code, Rule 229)[4].
- Gas or paraffin heaters and camping stoves can make carbon monoxide, which you can't see or smell[5].
Why do car windows steam up on the inside?
Warm air can hold more water vapour than cold air. In a closed vehicle on a cold night, the air picks up moisture from everyone breathing, from wet coats and boots, and from cooking if you're in a camper. The glass, meanwhile, is the coldest surface in the vehicle: it's thin, and on a clear night it loses heat to the sky[3]. Where the air touching the glass cools below its dew point, the extra vapour comes out as droplets[1][2]. If the glass drops below freezing, that moisture can ice up on the inside. That's also why windows steam up faster on rainy days: wet coats, umbrellas and footwells add moisture quickly.
- Warm cabin air picks up moisture from breathing, wet coats and boots, and cooking.
- The glass is the coldest surface. Where it's below the air's dew point, the vapour turns to droplets.
- On clear, calm nights the glass loses heat to the sky, so it gets colder still.
- A little ventilation lets damp air out before it reaches the glass.
How do I stop condensation in my van overnight?
Stopping condensation in a van, camper or car overnight comes down to these steps, roughly in order of how much they help:
- Ventilate a little, all night. A window cracked open or a roof vent lets damp air escape. This matters most, and no blind or moisture trap replaces it.
- Keep wet things out. If you can, don't dry clothes, towels or the dog inside overnight.
- Cook with ventilation. Open a vent or the door and put lids on pans. Never cook or run a fuel heater in a closed vehicle (see the carbon monoxide warning below).
- Keep warm air off the cold glass. Insulated thermal blinds or screens put a layer between the cabin and the windows.
- Soak up what's left. Moisture traps help, or a small dehumidifier if you're on hook-up.
- Wipe in the morning, and keep the glass clean. Use a microfibre cloth on the glass, and behind the blinds, then wring it out outside so the water doesn't soak into the seals and trim. A greasy film on the inside of the glass holds on to mist, so clean it now and then.
- Clear every window before you drive (see below).
Which fix does what?
| Fix | What it does | Best for |
|---|---|---|
| A little ventilation | Lets damp air out of the vehicle | Every vehicle, every night |
| Keeping wet things out | Stops moisture getting in to begin with | Vans, campers, anyone with a dog |
| Thermal blinds or screens | Keep warm, damp cabin air off the cold glass | Sleeping in a car, van or camper |
| Moisture absorbers or a dehumidifier | Soak up some of the moisture already in the air | Parked cars; campers on hook-up |
| Demister and air con | Dry the air and warm the glass while the engine runs | Clearing the windows before you drive |
What can I put in my car to stop condensation?
For condensation in a car you use every day, the quickest fix is the demister and air conditioning set to fresh air, plus clean glass: dirty glass holds on to mist. Moisture absorbers, such as silica gel bags, help in a car that's parked for a long time. If you sleep in your car, or it's parked overnight in the cold, thermal blinds keep warm, damp air off the windows. Take them out before you drive.
How do I demist a car windscreen quickly?
If your car windows are steaming up as you set off, turn the heater up, switch the air conditioning on, set the air to come in from outside rather than recirculate, and point it at the windscreen. Air con dries the air, and recirculating keeps the damp air inside, so fresh air with air con clears the glass fastest. Switch on the heated rear window too, and wait until every window is clear before you set off[4].
Why does my car keep getting condensation inside?
If your car windows keep misting up every day, even after a dry night, something is probably letting water in or keeping it there. Things worth checking:
- Wet carpets or footwells, from wet shoes or a spill that never dried out
- Worn door, boot or window seals, or a sunroof drain that's blocked
- A blocked pollen filter (also called a cabin filter), which cuts the airflow through the vents
Dry the carpets out, and ask a garage to look at the seals and filter if it carries on.
How do I stop condensation in the back of a work van?
The back of a work van often has bare metal panels, which get just as cold as the glass and drip in the same way. Ventilation and keeping wet kit out of the van matter most. Covering the windows and insulating the panels leaves fewer cold surfaces for moisture to settle on.
Do thermal blinds stop condensation?
They cut it down a lot, but they don't take moisture out of the air. As our FAQ puts it: "Add a little ventilation and you'll wake up to dry windows."
- Infrared-reflective coated foil: reflects radiant heat.
- A double layer of trapped air pockets: slows heat moving through the blind.
- A polyester layer that resists damp and UV.
- About 13mm thick in all, and stiff enough to hold its own shape, so it needs fewer suction cups.
The layers are drawn pulled apart so you can see them. In the blind they're one piece.
Our blinds are about 13mm thick, in three layers: an infrared-reflective coated foil, a double layer of trapped air pockets, and a polyester layer that resists damp and UV. Our parent company, Macaw, has made temperature-controlled packaging for medicines in transit since 2002, and the material comes from that work. The trapped air slows heat moving through the blind and the foil reflects radiant heat, so the warm, damp cabin air is kept off the cold windows.
What our blinds do, and don't do
- They do keep warm, damp cabin air off the cold glass, which cuts condensation on your side of the blind a lot. They also add privacy, keep the vehicle warmer on cold nights and cooler on sunny days, and stop the sun bleaching the interior.
- They don't take moisture out of the air. Because the blind keeps the cabin's warmth away from the glass, the glass behind it can get colder, and if damp air gets behind the blind, some moisture can still collect there.
- So: keep a little ventilation going, and wipe behind the blinds in the morning.
Read more about what's inside our thermal blinds.
Which way should thermal blinds face in winter?
Silver foil facing in. Our standard blinds clip in either way round, so you can turn them to suit the season. In winter, turn them so the silver foil faces into the vehicle: the foil reflects radiant heat, so facing in, it sends warmth from you and your heater back into the cabin instead of letting it out through the glass. In summer, turn them back so the foil faces out and reflects the sun's heat away.
The trapped air in the middle insulates whichever way round the blind goes, and for condensation, a little ventilation still matters more than which way it faces. Stealth blinds aren't reversible: the black side stays facing out all year.
Carbon monoxide: never heat or cook in a closed vehicle
Gas or paraffin heaters, camping stoves and barbecues can produce carbon monoxide, a poisonous gas you can't see, smell or taste[5][6]. The NHS warns that using barbecues or camping stoves inside can cause a build-up of it[5], and the HSE lists poorly ventilated appliances among the causes of carbon monoxide poisoning[6]. In a van or camper, only use heaters designed and fitted for vehicles, keep the ventilation open, and fit a carbon monoxide alarm. If you get a headache or feel dizzy or sick, stop using the heater or stove, get outside and get medical advice: call NHS 111, or 999 if someone is struggling to breathe, confused or unconscious[5].
Before you drive
Highway Code Rule 229 says that before you set off you must be able to see, so clear all snow and ice from all your windows, and make sure the windows are demisted[4]. Take the blinds off the windscreen and front side windows before you drive. They're for when you're parked.
Questions people ask
Do thermal blinds stop condensation completely?
No. They cut it down a lot by keeping warm, damp air off the cold glass, but they don't take moisture out of the air. Add a little ventilation and wipe behind the blinds in the morning.
Why do my windows get wet on the inside, not the outside?
The air inside is warmer and wetter, from your breath, and the glass is cold. So the inside of the glass drops below the cabin air's dew point and water condenses on it.
Should I leave a window open overnight to stop condensation?
Yes, a little. A small gap or an open roof vent lets damp air escape, and it works best with the blinds in to keep the warm air off the glass. Keep the gap small so you stay secure and warm.
Why is my windscreen frozen on the inside?
It's condensation that has frozen. Moisture from the air inside settles on the glass, and when the glass drops below freezing it turns to ice. Less moisture inside and a little ventilation stop it forming.
Should I use the air con to demist my windows?
Yes. Air conditioning dries the air, so with the heater on, the air con on and fresh air coming in (not recirculated), the windows clear faster than with heat alone.
Can I drive with the blinds in?
Not on the windscreen or front side windows. You must be able to see clearly out of your windows before you drive (Highway Code Rule 229).
Do you make blinds for my vehicle?
Use the vehicle picker, or WhatsApp us your make, model and year. We make blinds up to 1.6m wide in one piece, and odd windows can be templated with our £10 kit or at our Redditch workshop.
Sources
Wake up to drier windows
Made-to-measure thermal blinds for cars, vans, campers and motorhomes, up to 1.6m wide in one piece.
Odd-shaped windows? Our £10 templating kit lets you trace them at home. Or come to our Redditch workshop and we'll make your blinds while you wait, usually in 1 to 3 hours (Tuesday to Friday, book first).