Cold, damp mornings and a windscreen that mists over the moment you get in: it is one of the most common winter annoyances, and it is a safety issue as well as a nuisance. Here is what is happening and how to fix it properly.
Why car windows fog up
Fogging is condensation. Warm, moist air inside the car (your breath, wet coats, damp carpets) meets cold glass and the moisture condenses into tiny droplets that scatter light. Dirty glass makes it worse, because the film of grime gives the droplets something to cling to.
Quick fix when it is already fogged
- Turn the heater to the windscreen setting and run the air conditioning, which dries the air.
- Use fresh air rather than recirculation so damp air can leave.
- Crack a window briefly to let moisture out.
This clears the glass, but it does not stop it happening tomorrow.
The long-term fix: clean glass plus an anti-fog film
- Clean the inside glass first. Use Vonixx Glazy and a clean microfibre. Interior glass collects a greasy film from vinyl and plastics, and anti-fog will not work properly over it.
- Apply Glazy Anti-Fog to a microfibre, not the glass. Spray Vonixx Glazy Anti-Fog onto the cloth. This avoids overspray on the dashboard and trim.
- Wipe edge to edge. Cover the whole pane evenly.
- Buff dry. Use a second clean, dry microfibre until the glass is clear.
The treatment leaves a thin film that stops moisture forming droplets. Repeat it every few weeks through the winter.
Reduce moisture in the cabin
- Shake out wet coats and umbrellas before getting in.
- Dry damp footwell mats and carpets, which release moisture for days.
- Check door seals and drain areas for leaks if the carpets are persistently wet.
- Replace the cabin filter if airflow feels weak.
Persistently damp carpets are also a cause of musty smells, which our interior smell guide covers.
Frequently asked questions
Why do my windows fog up even with the heater on?
Usually because there is too much moisture in the cabin or the glass is dirty. Clean the glass and dry out the interior.
Can I put anti-fog on the outside?
No. Fogging happens on the inside. Use Glazy on the outside for a clean windscreen.
How often should I reapply?
Every few weeks through winter, or whenever you notice misting returning.
Products mentioned in this guide
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