Van Life Insulation UK: Complete Guide to Materials & Installation for British Weather
Insulation is the most misunderstood part of a UK van conversion. Spend £500 on the wrong material and your van will still be cold, damp, and mouldy. Spend £200 on the right material and you will sleep warm through a Scottish winter.
I have insulated two vans with three different materials. The first van used reflective bubble wrap (the most common mistake in UK van builds) and was a damp, cold nightmare. The second used closed-cell foam + PIR boards and is comfortable year-round. This guide covers what actually works in UK conditions.
Why UK Van Insulation Is Different
UK van insulation faces three specific challenges that make it different from campervans in sunnier climates:
- Cold + wet: The UK rarely goes below -5°C, but the humidity is consistently 70–90%. Cold is manageable. Cold + damp creates condensation, which rots the van and grows mould in the cupboards.
- Short winter days: Limited solar gain means the van does not warm up during the day to offset night-time cooling.
- Vibration: Unlike a house, a van flexes and vibrates. Rigid insulation must be securely fixed or it will crack and separate.
What NOT to Use
Reflective bubble wrap (Silver Screens, Reflectix, any foil-faced bubble material). This is sold as "insulation" in van conversion shops but has an R-value of approximately 0.1 when in direct contact with the van wall. The air gap it needs to work (25mm+) does not exist in a van cavity. Worse, it traps moisture against the metal, causing rust. Do not use it.
Standard fibreglass loft insulation. Absorbs water from condensation, sags under vibration, and the fibres settle over time. It also causes skin and lung irritation during installation. Designed for attics, not moving vehicles.
Spray foam (closed-cell polyurethane) is excellent but expensive (£400–800 for a medium van) and requires professional installation. A mistake means acetone and a lot of scraping.
What to Use
Best All-Rounder: Closed-Cell Foam + PIR Boards
This is the combination used in most successful UK van builds.
Walls: 10mm closed-cell foam (Armaflex, Kaiflex, or generic EPDM foam). It cuts with scissors, glues with spray adhesive, and conforms to curved van walls. It does not absorb moisture. Cost: ~£50–100 for a medium van.
Ceiling: 10mm or 19mm closed-cell foam. Pack the gaps between roof ribs with foam strips.
Floor: 25mm PIR board (Celotex, Kingspan, or similar). PIR has the highest R-value per mm. Cut to fit between floor ribs, seal edges with aluminium tape. Cost: ~£40–80 for a medium van.
Cavity filling: For large gaps behind wheel arches, use Dodo Mat Super Liner or similar closed-cell foam sheeting. Do not use expanding foam cans — they absorb moisture over time.
Natural Alternative: Sheep Wool
Thermafleece or Black Mountain sheep wool insulation is breathable, handles moisture well, and is easy to install. It costs ~£100–150 for a medium van. The downsides: it is harder to find (specialist suppliers), slightly lower R-value per mm than PIR, and can attract moths if not properly sealed.
Budget Option: PIR Boards Only
If budget is tight, use 25mm PIR boards everywhere. It is rigid, so it does not conform to curved walls without scoring the back. Fill gaps with foam strips or aluminium tape. Cost: ~£80–120 for a medium van.
The Order of Insulation Installation
-
Rust treatment: Before any insulation goes in, clean the bare metal with a wire brush, treat rust with Jenolite or Kurust, prime with red oxide, and paint. Do not skip this — once the insulation is in, you will not see this metal for years.
-
Sound deadening: Apply butyl sound deadening (Noico, Silent Coat, Dodo Mat) to large flat panels — the roof, side panels, and doors. Cover about 30% of the surface in 10x10cm patches. This stops drumming noise, not heat loss. Cost: £30–60.
-
Walls: Cut closed-cell foam to shape, glue with spray adhesive, press into place. Seal seams with aluminium tape. Pay special attention to the cab bulkhead area — this is a major heat loss point. Use thicker foam here.
-
Ceiling: Same as walls. The roof loses the most heat in winter and gains the most in summer. Double-layer the foam if there is space between the roof ribs and lining.
-
Floor: Fit 25mm PIR boards between floor ribs. Tape all seams. If ribs are shallow (Transit Custom has 18mm ribs), use 12mm foam between ribs and 12mm PIR sheeting on top before the plywood subfloor. This creates a thermal break.
-
Vapour barrier: This is critical and often missed. Before fitting your ply lining, install a continuous vapour barrier on the warm side of the insulation (the living space side). Use 0.1mm polythene sheeting or foil tape over all foam board seams. This prevents warm, moist air from the living space reaching the cold van metal, where it would condense.
-
Battening: Screw 20x20mm timber battens through the insulation and vapour barrier into the van ribs. These support your ply lining and maintain an air gap between the vapour barrier and the lining.
Condensation Management
Even perfect insulation alone does not stop condensation. In a van, moisture is produced by your breath (1–2L per night per person), cooking, washing, and wet clothes. This moisture must go somewhere.
The winning formula:
- Airtight vapour barrier on the warm side
- Ventilation: a roof vent (MaxxAir or Fiamma Turbo) running on extract 24/7 in winter
- Directed heat: the diesel heater draws in outside air (combustion intake is external) and heats the interior air, which then absorbs moisture and carries it to the vent
Insulation Cost for Common UK Vans
| Van | Material | Cost | Time |
|---|---|---|---|
| VW Transporter T6 | 10mm closed-cell + 25mm PIR floor | £120–180 | 1 day |
| Ford Transit Custom (medium roof) | 10mm closed-cell + 25mm PIR floor | £150–250 | 1–2 days |
| Mercedes Sprinter (LWB high roof) | 10mm closed-cell + 25mm PIR floor | £250–400 | 2–3 days |
| Fiat Ducato / Citroen Relay | 10mm closed-cell + 25mm PIR floor | £200–350 | 2 days |
FAQ
Q: How do I insulate the cab area? A: The cab roof and doors are best insulated with 10mm closed-cell foam glued to the panels, covered with a tailored cab curtain (£30–80) or thermal blind. The cab floor can be insulated with 25mm PIR under the rubber mat.
Q: Do I need to insulate the wheel arches? A: Yes. Wheel arches are major cold spots and condensation points. Use closed-cell foam, shaped around the arch. Seal the foam to the arch with spray adhesive and tape.
Q: Should I insulate under the van? A: Spray foam under the floor pan is common in the US but not recommended for UK vans. It traps moisture against the floor, causes rust, and makes future repairs difficult. Focus on insulating the interior floor.
Q: What about thermal cameras windows? A: Cheaper than double-glazed windows and almost as effective. Reflective film or a thermal curtain on the inside of the windscreen cuts the biggest thermal bridge in a van overnight.
Q: How do I know if my insulation is working? A: A qualitative test: on a cold morning, touch the interior of the van wall (under the lining). If it feels cold to the touch, either the insulation is too thin, or the vapour barrier is allowing moist air through. Condensation on the insulation side of the vapour barrier means the barrier failed.
Q: Can I add insulation to a finished conversion? A: Not easily. If the van was not properly insulated during the build, the options are: strip the lining and start again, or add a thermal curtain layer and focus on managing condensation through ventilation.
