Short answer: good campervan insulation covers the floor, roof, side walls and doors, leaves no air pockets against the metal, and deals with moisture. Most UK builds mix materials: rigid foam board on flat panels and the floor, sheep's wool or fibre roll in cavities, and thin foil-backed foam where depth is tight. Insulate early, after windows and before lining, and keep the van ventilated.
Why insulation matters in a UK van
A bare van is a metal box. In a British winter the walls get cold, and every breath, kettle and wet coat puts moisture into the air. When that warm, damp air meets cold metal, it condenses. Insulation slows heat loss, so your heater works less, and keeps the inside surfaces warmer, so less water forms on them. It also cuts road and rain noise.
Camplify's guide puts the aim neatly: move the dew point away from the van wall so moisture cannot collect between the metal and the insulation. Any air pocket against the steel is where condensation, rust and rot start.
Campervan insulation materials compared
These notes come from Camplify's and Just Kampers Insurance's guides. Neither crowns one best material, and nor would we.
| Material | Good for | Watch out for |
|---|---|---|
| Sheep's wool (for example Thermafleece) | Cavities and curved panels; handles moisture well; some sound proofing | Costs more; fix with spray adhesive |
| Rigid foam board (PIR, XPS) | Flat walls, roof and under the floor; high R-value for its thickness; does not compress | Hard to fit to curves; Camplify flags polystyrene's fire safety record and squeaks |
| Foil-faced self-adhesive foam (7 to 10mm) | Shallow panels, doors, edges; no glue needed | Thin, so less insulation on its own |
| Closed-cell foam (Armaflex type) | Thermal bridges and ribs; absorbs very little moisture | Rigid versions are harder to work |
| Polyester fibre roll | Stuffing cavities; usually sold in 50mm rolls; often recycled | Needs a cover to keep it in place |
| Glass wool or rockwool | Low cost | Absorbs moisture, needs a vapour barrier, irritates skin; wear a mask |
| Expanding spray foam | Small gaps and holes | Overfilled panels make lining hard; Camplify advises against it for thermal bridges |
What we would do again: foam board on the big flat panels and floor, wool in the ribs and awkward cavities, foil-backed foam on the doors. That is our preference, not a rule.
How to fit it
Insulation goes in after the strip out and window cutting, and before the floor and lining. Our conversion steps guide shows where it sits in the whole build. The method below follows Just Kampers Insurance's step by step.
- Plan the runs first. Decide where every cable and pipe goes and fit conduit before insulating. Getting a cable behind finished insulation later is miserable.
- Clean and prepare. Remove moisture, swarf from window cutting, oil and grease, and treat rust. Camplify stresses the surface must be completely dry. If you are using foil-backed bitumen sound deadening, it goes on now, directly on the panels.
- Batten the floor. Keep battens level and space them to the width of your insulation board. Route cables between the battens.
- Walls, ceiling and doors. Use board or foil-backed foam on large areas and fibre or wool in cavities. With foil-backed boards, Just Kampers Insurance suggests a 20mm gap to the van skin so the foil can reflect radiant heat; offcuts make good spacers.
- Fill the cavities. Tear wool or fibre into pieces and fill the gaps, without packing it tight: the trapped air is what keeps the heat in.
- Seal. Fit a vapour barrier over the insulation if your material needs one, and tape all edges with aluminium tape.
The floor
Insulating the floor is debated, because it can trap moisture. Camplify suggests laying floor insulation without glue, so the floor can come up to check for rust, and letting the weight of the floor and furniture hold it.
Windows and thermal bridges
Glass is where most heat goes. Camplify suggests removable insulated window covers. Metal ribs and pillars that join inside to outside are thermal bridges; cover the big ones with closed-cell foam.
Sound deadening
Sound deadening is a separate job from insulation, though the two overlap. Foil-backed bitumen mat goes straight onto large flat panels before anything else, because it has to touch the metal to stop it drumming. You do not need to cover every panel; the big flat skins on the sides, roof and rear doors make most of the noise. Sheep's wool adds some sound proofing on top.
Doors and the cab
Camplify lists door panels as worth insulating after the floor, roof and walls. Use thin foil-backed foam inside the door skins so the trim still fits, and seal edges with foil tape. If the cab is open to the living space, a thick curtain behind the seats keeps a lot of heat in at night.
Condensation, vapour barriers and air gaps
Insulation alone will not stop condensation. Three things help:
- No air pockets against the metal. Stick insulation fully to the panel or fill the cavity, so warm air cannot reach cold steel.
- A vapour barrier where it is needed. Glass wool definitely needs one. Sealing a van perfectly is hard, and moisture that does get behind a barrier can be trapped, which is one reason many builders prefer wool, which tolerates moisture.
- Ventilation and dry heat. A roof vent or fan and a dry air heater do more for damp than any material choice. Our campervan in winter guide has more.
What it costs
Camplify estimates insulation at £250 to £300 for a van, and Just Kampers Insurance at about £300. That makes it one of the cheaper stages, and one of the hardest to redo, so it is not the place to save. See the full van conversion cost guide for every line item. If you want to track it, Build expenses in Roam scans receipts and keeps a budget per stage, in the app now.
Questions
What is the best insulation for a campervan in the UK?
There is no single best. Foam board gives the most insulation per millimetre on flat panels, sheep's wool handles moisture well in cavities, and thin foil-backed foam suits shallow doors. Most builds mix them.
Do I need a vapour barrier in a campervan?
Yes if you use glass wool or similar materials that absorb moisture. With closed-cell foam or wool, opinions differ. Whatever you choose, avoid air gaps against the metal and keep the van ventilated.
Should I insulate the floor of my van?
Many people do, with board between level battens. It is debated because it can trap moisture, so lay it so the floor can be lifted to check for rust.
How thick should campervan insulation be?
It is limited by panel depth. Self-adhesive foil foam is usually 7 to 10mm and fibre rolls often 50mm; fill the depth you have without compressing it.
When in the build should I insulate my van?
After the strip out and after cutting windows and vents, but before the floor, electrics and lining. Run cable conduit and pipe routes first so nothing has to be pulled back out later. Insulating early is the single easiest way to avoid redoing work.