Campervan insulation costs centimetres before it costs euros
· 7 min read
Insulation guides argue about materials as if the van were infinitely large. It isn't. Every millimetre of insulation is taken off the inside, twice per axis — and the budget is brutally small: 25 mm on each wall turns a Fiat Ducato's 1.87 m of interior width into 1.82 m, which is 4 cm less than a standard 1.86 m mattress. On the only large van that fits a bed across, the insulation decision and the bed decision are the same decision.
So before comparing thermal numbers, decide what the centimetres are worth. This guide does both sides of that trade.
The two equations
Width: interior width − 2 × (insulation + cladding) = bed-across budget. Cladding is 3–6 mm ply or textile; with 25 mm insulation you lose ~6 cm of width in total. A Ducato drops below the mattress line; a Crafter (1.83 m) or Daily (1.80 m) that needed wheel-box flares anyway keeps needing them. Full width table for every van is in the dimensions comparison.
Height: floor (20 mm insulation + 12 mm ply ≈ 3.5 cm) + ceiling (25 mm + cladding ≈ 3 cm) ≈ 6–7 cm of headroom. That is the difference between standing and stooping for anyone within 7 cm of their van's raw interior height — check yours against the same table before choosing floor build-up.
Warmth per centimetre
Insulating power is thickness ÷ lambda (thermal conductivity, W/mK — lower is better). Manufacturer-datasheet ballparks:
| Material | λ (W/mK) | Typical build | To match 25 mm PIR you need |
|---|---|---|---|
| PIR/PUR board | ~0.022–0.028 | 20–30 mm floor, flat wall fields | 25 mm (baseline) |
| XPS board | ~0.032–0.038 | 20–30 mm floor | ~35 mm |
| Elastomeric foam (Armaflex type) | ~0.033–0.040 | 19–25 mm glued to walls/ceiling | ~35–40 mm |
| Sheep wool | ~0.035–0.045 | 50 mm stuffed in rib cavities | ~40–45 mm |
| Polyester batting (Thinsulate type) | ~0.040–0.045 | 40–50 mm in cavities | ~45 mm |
Read the last column as a space price. Boards buy the most warmth per centimetre but only fit flat fields; flexible foam follows the van's curves at a ~40% thickness premium; wool and batting are cavity fillers — they mostly occupy space the ribs already stole, which is why cavity insulation is nearly free in centimetres and why most builds combine it with a thin continuous foam layer over the ribs.
Where the centimetres matter, and where they don't
- Roof: spend freely. Warm air stratifies under the ceiling, so the roof carries the biggest temperature difference — and headroom over the aisle is the only place you need it. Over the bed and galley, 25 mm costs nothing you use.
- Walls at mattress height: count twice. This is the bed-across zone. If the transverse bed is the plan, thin high-performance foam here (or cavity-only) is the correct call even if the rest of the wall gets more.
- Floor: comfort, not physics. The temperature difference through the floor is the smallest in the van; 20 mm mostly buys warm feet. If headroom is marginal, the floor is the first place to go thin.
- None of it works without airflow. Insulation slows heat loss; it does not stop the moisture you exhale. The condensation half of the problem is ventilation — sized in the EN 721 guide.
Plan it before you glue it
The planner has an insulation-thickness setting that shrinks the usable interior on every wall at once — set 25 mm and watch whether your bed, kitchen and walkway still fit before anything is cut or glued. It is the cheapest insulation mistake you will ever make. Pick your van and try it.
