Campervan Insulation: The Complete Guide

Overview

Ask experienced van builders what they would never skimp on and insulation comes up before almost anything else. It is cheap compared with nearly every other part of a campervan conversion, it is buried behind the walls where it can never easily be upgraded, and it determines how the finished build feels every single day — warm in January, bearable in July, quieter on the motorway, and dry inside when two people are cooking with the doors shut.

This guide compares the main campervan insulation materials honestly, tackles the vapour barrier question (and the condensation problem behind it), and covers each area plus costs.

Why Insulation Matters More Than Heating

A bare metal van is close to the worst case for keeping heat in: a thin steel box with big glass areas and metal ribs running through every wall. Heat pours out through the panels in winter, and heat from the sun pours in through metal and glass in summer.

You can fight that with a bigger heater, but it is a losing game. Heating an uninsulated shell is like running a bath with the plug out — the heater cycles constantly, burns more fuel, and the moment it stops the temperature crashes. Good thermal insulation means a small 2kW diesel heater holds a comfortable environment at a whisper, condensation drops dramatically, and the living space stays cooler in summer too. Insulate first, then size the heating.

How Heat Escapes a Van

Three mechanisms of heat transfer, all of them at work in a metal box:

A good scheme deals with all three: bulk insulation slows conduction, sealing gaps controls air movement, and aluminium foil facings reflect radiant heat where there is an air gap for them to work across.

Campervan Insulation Materials Compared

There is no single best insulation — there are trade-offs. The honest comparison:

PIR rigid boards (Celotex and Kingspan are the familiar names) — foil-faced insulation sheets with the best thermal performance per millimetre of the common options, cheap, and available from any builders' merchant. The catch: rigid boards only suit flat sections. Cut to fit the large panels and the floor they are excellent; forced against curved van walls with gaps around them, much of the benefit disappears. Typical thicknesses are 25mm on walls and up to 50mm in floors and ceilings where space allows.

XPS foam board — extruded polystyrene, similar use case to PIR with slightly lower thermal properties but better moisture resistance and compressive strength, which makes XPS a favourite for floor insulation under ply.

Sheep's wool — natural wool insulation sold in rolls. Slightly lower performance per millimetre than PIR, but it stuffs beautifully into curved cavities, ribs and awkward voids, and — its trump card — it manages moisture, absorbing and releasing water vapour without rotting or slumping. Environmentally friendly too. It costs more than PIR for the same job.

Synthetic wool (Thinsulate-type products) — polyester-style fibre battings, often self-adhesive backed, made specifically for vehicles. Easy to fit into a cavity and does not hold water. Performance per millimetre is modest, so it shines in thin, curved sections — doors, pillars, wheel arches.

Bubble foil and multifoil products — honest assessment: widely sold, widely misunderstood. Foil insulation works as a radiant barrier only when it faces an air gap; bubble wrap style foil squashed directly between metal and cladding does very little. Useful for window covers and as a supplementary layer, not as your primary van insulation.

A note on numbers: materials are compared by R-value (resistance to heat flow — higher is better) or lambda value (conductivity — lower is better). Do not get lost in the decimals: a well-installed average material beats a badly installed excellent one, so fit as much thickness as the build allows and fit it without gaps.

Thermal Bridging

Insulating the panels but leaving the metal ribs bare is like wearing a good coat with holes along every seam. Steel ribs conduct heat straight past your insulation from the warm inner skin to the cold outer skin — that is thermal bridging, and it shows up as cold stripes and damp lines along walls and ceiling.

You cannot eliminate it entirely, but you can blunt it: run a thin continuous layer (synthetic wool or thin foam) across the ribs before cladding, fit timber battens so wall boards never touch metal, and fill inside each rib cavity you can reach.

Vapour Barriers and Condensation — the Big One

This is the part that ruins vans. Everyone aboard breathes out water vapour all night; cooking and wet gear add more. Warm moist air migrates toward cold surfaces, and when it reaches cold steel it condenses into liquid water. Trapped behind insulation, that moisture sits against the metal, and over the years the result is mould, musty smells and eventually rust.

The theory says: create a vapour barrier — a continuous membrane on the warm side of the insulation, taped at every joint — so moist air never reaches the cold metal. The awkward truth is that a perfect vapour barrier is close to impossible in a vehicle. Every screw, cable and fixing punctures it, and a leaky one can be worse than none, trapping moisture in the walls instead of letting them dry out. (American guides call it a vapor barrier — same thing, same debate.)

So the practical approach used in most UK conversions is:

Area by Area: Floor, Walls, Ceiling and Windows

Ceiling first in priority. Warm air collects at the roof, so this is where insulation earns most. Insulate between the roof ribs — boards on flat sections, wool stuffed in the gaps — treat the ribs, then clad.

Walls. Board the big flat panels with insulation sheets, stuff wool or synthetic batting into every cavity and door skin, and do not forget the wheel arches — bare arches are both a thermal hole and a drum for road noise.

Floor. Cold rising from bare metal underfoot is miserable, and damp forms under flooring laid straight onto steel. The usual build: thin battens, rigid board (XPS or PIR) between them, then a ply subfloor and the finished floor. Even 25mm underfoot makes a real difference.

Windows. Glass is by far the worst-performing surface in the build and no wall treatment fixes it. Fitted thermal window covers transform winter comfort and cut misting on the glass, and external silver screens for the cab are the best-value warmth upgrade after the insulation itself.

Sound Deadening

Not strictly thermal work, but fitted at the same stage, so plan them together. Sound deadening mats are heavy butyl panels stuck directly to the large metal panels to stop them resonating — covering roughly a quarter to a half of each panel is enough to kill the drumming and noticeably reduce road noise. Deadening goes on first, insulation over the top. The difference between a soundproofed build and a bare one is obvious within the first mile.

DIY or Professional?

Insulating a campervan is one of the most DIY-friendly stages of converting a van: the materials are cheap, the tools are basic (knife, saw, spray adhesive, foil tape), and mistakes are rarely dangerous — just cold. If you are self-building, spend your effort on fit and sealing, not spreadsheet comparisons.

The case for professionals is the system, not the stuffing. A good converter designs insulation, vapour strategy, heating and ventilation together, knows where damp traps form in your specific base vehicle, and warranties the finished conversion. If a converter's quote glosses over insulation — which material, what thickness, what ventilation — treat it as a red flag and ask. Every reputable converter in our directory can tell you exactly what goes behind their walls.

What Campervan Insulation Costs

Broad, honest bands for insulating a whole vehicle yourself:

Whichever route you take: the money at this stage is small, the consequences are permanent, and nobody has ever finished a winter trip wishing their motorhome or camper had less insulation.

Frequently Asked Questions

What is the best insulation for a campervan?

There is no single winner. PIR boards give the best performance per millimetre on flat panels and floors; sheep's wool or synthetic batting fills curved cavities and manages moisture. Most good conversions combine both. The best insulation is whichever you can fit continuously, without gaps.

Do you really need to insulate a campervan?

For UK use, yes. An uninsulated van is cold from autumn to spring, hot in summer, noisy, and streams with condensation whenever someone sleeps in it. Insulation costs a few hundred pounds and improves every night you ever spend aboard.

How thick should campervan insulation be?

As thick as the space allows. Typical UK builds use 25mm boards on walls, 25–50mm in the ceiling and floor, and stuffed wool where boards cannot follow the curves. Beyond about 50mm you hit diminishing returns and start eating living space.

Do I need a vapour barrier in my campervan?

A perfect one is nearly impossible in a vehicle, and a bad one traps moisture. Use moisture-tolerant materials, tape the board joints, and prioritise ventilation and gentle heating — that combination keeps the interior dry more reliably than plastic sheeting alone.

Can I use loft insulation in my van?

Avoid it. Household fibreglass slumps in a moving vehicle and holds moisture against the metal once damp. Van-appropriate options — PIR, XPS, sheep's wool, synthetic batting — cost only a little more and are designed to cope.