Insulating Your Van for UK Winters
Insulation is the single most important part of a campervan conversion that you cannot easily fix later. Get it right and your van stays warm in winter, cool in summer, and condensation-free year-round. Get it wrong and you fight damp, cold, and mould forever.
Insulation Materials Compared
Closed-cell foam boards (Celotex, Kingspan, XPS) — The best choice for most DIY converters. High R-value per mm (about 0.022 W/mK), vapour-impermeable (moisture does not pass through), easy to cut to shape. Cut panels to fit between van ribs, seal edges with aluminium tape. Cost: £300-600 for a panel van.
Spray foam — The best thermal performance. Fills every cavity and creates an airtight seal. Professional application recommended. You cannot remove it if you need to access the van bodywork. Cost: £800-1,500 for professional application.
Thinsulate / felt — Good for DIY, easy to install, breathable (moisture passes through). Lower R-value than foam board (needs thicker sections). Good for walls where you need flexibility. Cost: £200-400.
Sheep's wool — Natural, sustainable, breathable. Handles moisture well. Needs a vapour barrier. Lower R-value. Cost: £300-600.
Reflective foil — Reflects radiant heat, poor for conductive heat loss. Use as a secondary layer or vapour barrier, not as primary insulation. Cost: £50-100.
The Recommended UK Setup
The most effective and common approach for UK van insulation:
- Ceiling — 50mm closed-cell foam board. Biggest heat loss area in a van.
- Walls — 25-50mm foam board or Thinsulate between the metal ribs.
- Floor — 25mm foam board under the plywood floor, plus a layer of foil-backed insulation on the ply.
- Gaps — Spray foam or expanding foam tape around windows, doors, and roof vents.
- Vapour barrier — Aluminium tape over all foam board joints. On Thinsulate, a vapour barrier sheet on the warm side (inside of the van).
Total cost: £500-1,000 for materials.
Condensation Prevention
Breathable insulation (Thinsulate, sheep's wool) allows moisture to pass through and dry out. Non-breathable insulation (foam board, spray foam) needs a perfect vapour barrier — any gap allows moisture to condense on the cold metal behind the insulation.
Realistically, van insulation in the UK needs ventilation as well. A roof vent with a rain cover and a low-level vent create airflow that carries moist air out. Without ventilation, no insulation will prevent condensation entirely.
How Much to Install
- 50mm ceiling — This is the most important area. Heat rises and escapes through the roof most quickly.
- 25mm walls — Adequate for walls. More if you have the space.
- 25mm floor — The floor loses heat to the ground. Important but less critical than the ceiling.
Deeper sections are better for thermal performance but reduce interior space. In a typical panel van, 50mm on the ceiling and 25mm on walls and floor is the balance most converters choose.
Final Thoughts
Closed-cell foam board with careful sealing is the most reliable approach for UK van insulation. It is effective, affordable, and DIY-friendly. Thinsulate is a good alternative for walls if you want breathability. Whatever you choose, do not skimp on the vapour barrier and plan for ventilation. Insulation without ventilation leads to condensation, which leads to mould, which ruins your van and your health.
