Building
Insulating a van: what works, what does not, and where condensation comes from
Insulation rarely fails on the material and almost always on the moisture. A van is a closed metal box in which two people breathe out roughly a litre of water per night; everything you put against the wall decides where that water ends up. This article is about that choice, and about the mistakes you only see after two winters.
Updated on 16 min read
The problem is not the cold
Warm air holds more water than cold air. Inside your van it is warm and humid; against the panel it is cold. The moment that humid air reaches the cold steel, the water condenses — exactly where you cannot reach it. Insulation that lets air through merely relocates the problem: the water then condenses behind the insulation instead of on it, and there it never dries out.
All three approaches below work, and they all work for the same reason: humid indoor air never reaches the cold panel. Keep to that one rule and you are fine — whichever material you choose.
The three workable approaches
| Approach | Strong point | Weak point |
|---|---|---|
| Closed-cell rubber, glued | Seals itself, so no separate vapour barrier is needed. Stays put, including on the roof. | Expensive, and you have to work seamlessly: every open seam is a leak. |
| Rigid foam board in the cavities | Cheap per centimetre and easy to cut to size. | Every edge must be sealed: leave a gap and the air behind it cools and condenses there. |
| Sheep wool with a vapour-control layer | Buffers moisture and releases it again, forgiving of mistakes. | Works only with a properly taped foil on the inside. Without it, it is the worst of the three. |
The materials by their own names
In the shop and on forums these materials go by different names than in a building textbook. Below is what you will run into, which category it belongs to, and whether it has a place in a van.
| What you run into | What it is | Verdict |
|---|---|---|
| Closed-cell rubber, often sold under brand names such as Armaflex | Vapour-tight in itself, self-adhesive, follows every curve | The safest choice in a van. Expensive, and you must work seamlessly. |
| PIR or PUR board with a foil facing | Rigid foam, high insulation value per centimetre | Fine in flat cavities. Every edge must be sealed, or it condenses behind. |
| Cork, as board or sprayed | Natural, damps sound as well, breathes | Works, but insulates less per centimetre, and sprayed cork is a job that rarely succeeds at home. |
| Sheep wool | Fibre insulation that buffers moisture | Good, but only with a carefully taped vapour barrier on the inside. |
| Glass wool or rock wool | Building insulation for cavities and lofts | Better kept for the house. In a van it settles under vibration and holds moisture against the panel. |
| Bubble foil or foil-faced bubble wrap | Thin material advertised with a high rating | The stated value only holds with still air layers on both sides, which you do not have. In a van it achieves almost nothing. |
| Spray foam from a can | Expanding filler foam | Only for small edges. In cavities it bows panels outward and traps moisture against the steel, permanently. |
Area by area: roof, floor, doors and cab
- 01
The roof
The largest area and in summer the hottest. Use a material that stays stuck without mechanical support here, because anything merely wedged against the roof will eventually drop. Keep the roof ribs clear if you may still fit a vent or a panel later, and note where they run.
- 02
The floor
Delivers the most comfort per centimetre of any area, because cold comes up through your feet. Compressive strength matters here: the material carries your furniture and you. Rigid foam between battens works well; soft material that compresses leaves your floor creaking in time.
- 03
The doors
Often skipped and immediately one of the biggest thermal bridges. Mind the drainage at the bottom: it must stay open, or water stands inside your door. Insulate the inner face of the outer skin, not the cavity the lock mechanism runs through.
- 04
The cab
The biggest hole in your insulation envelope, and not fixable with insulation: single glazing stays single glazing. An insulated curtain or bulkhead between cab and living space is the cheapest gain in the whole project here, and screens against the windscreen do more overnight than two extra centimetres on the wall.
- 05
Noise
Insulation against cold and damping against noise are two different things. Sound-deadening pads on the large, freely vibrating panels take the tinny ring out; a quarter of each panel is enough. Adding more costs weight and gains almost nothing.
Thermal bridges: where the heat really goes
Two extra centimetres of insulation on the wall gains far less than closing one thermal bridge. The biggest ones are almost always in the same places: the steel ribs in the wall you did not insulate, the floor you left untreated, the rear doors, and the opening to the cab. That last one is the biggest of all — a cab with single glazing is, in winter, effectively outdoors.
- Insulate the ribs too, even if there is only five millimetres of room. Five millimetres beats nothing.
- An insulated floor buys more comfort than an insulated roof: cold comes up through your feet, not down through your hair.
- A curtain or insulated screen between cab and living space is the cheapest gain in the entire project.
- Do not fill hollow sections: they are there for ventilation and water drainage.
The order in which to work
- 01
Strip out and de-rust
Strip all the lining out and treat everything that has rust. Whatever you skip now, you meet again in five years, under a cabinet.
- 02
Cables and glands first
Every cable, air duct and water line that runs behind the wall goes in now. A cable you forget is a cable you drill through a finished wall for later.
- 03
Damping pads on the large panels
Not for warmth but for noise. A quarter of each panel is enough; more is wasted weight and wasted money.
- 04
Fit the insulation
Fill the cavities, cover the ribs, seal the edges. Work top down, so nothing falls onto what you just finished.
- 05
Tape the vapour barrier
Only for materials that need one. Tape every cable or pipe penetration separately; a one-centimetre hole makes the whole membrane pointless.
- 06
Floor, then walls, then ceiling
Only then does the furniture go in. Re-measure the load space once this is done: that is the dimension you order on.
After insulating, your van is narrower, lower and shorter inside than the brochure says. That is exactly why our configurator asks for your own dimensions instead of blindly using factory figures.
Measure your van after insulating
What you need for this
We do not (yet) sell these parts separately. The list is here because this is what should be in your basket before you start.
- Closed-cell rubber on the roll, 19 or 25 mm
- Spray contact adhesive, rated to 90 °C
- Aluminium tape for seams and penetrations
- Sound-deadening pads for the large panels
- Cable glands for wall penetrations
Frequently asked questions
- Can I insulate my camper with bubble foil or glass wool?
- Neither. The rating printed on bubble foil only holds with still air layers on both sides, which a wall does not give you; in practice it achieves almost nothing. Glass wool settles under driving vibration, soaks up moisture and holds it against the panel, precisely the recipe for rust you only find when you strip everything out again.
- What do I insulate first: roof, walls or floor?
- In working order, top down, so nothing falls onto what you just finished: roof, then walls, then floor. In order of payoff it is the reverse, because the floor gives the most comfort per centimetre. And before all of it: the bulkhead or curtain to the cab, because that is where most heat is lost.
- How thick should the insulation be?
- Twenty to thirty millimetres on the walls is ample for European use. Thicker barely helps, because the remaining gain sits in the thermal bridges rather than in thickness, and every extra centimetre costs interior space on both sides that you will miss when the furniture goes in.
- Do I need a vapour barrier?
- Not with closed-cell rubber, provided you glue it seamlessly: the material is vapour-tight itself. With wool or open materials, yes — and it has to be genuinely sealed, including every cable penetration. A half-fitted vapour barrier is worse than none.
- Can I use spray foam?
- For sealing small edges and gaps: fine. For filling whole cavities: do not. It expands against the panel, can bow it outwards, traps moisture against the steel and can never be removed if you need access later.