Nobody starts a van build because they are excited about insulation. But ask anyone who has spent a January night in a poorly insulated van: this is the highest-leverage week of the entire project. Done right, it is invisible forever. Done wrong, it drips on you — literally.
The physics, in two paragraphs
A van is a metal box, and metal is a spectacular conductor of heat. In winter, every rib and panel is a bridge carrying your warmth outside; in summer, the same bridges work in reverse. Insulation works by breaking those bridges with materials that trap air.
The second problem is moisture. People exhale roughly a liter of water vapor per night, and warm humid air condenses on any cold metal surface it can reach. Your insulation plan is really a condensation plan.
The materials that earn their space
- Sheep's wool — manages moisture naturally, forgiving to install, no protective gear needed. Our default recommendation for walls and hard-to-reach cavities.
- Polyiso foam board — the highest R-value per inch for flat surfaces like the ceiling and floor, where every centimeter of headroom counts.
- 3M Thinsulate — thin, hydrophobic, and easy to glue into door panels and pillars where board will not bend.
What we skip: spray foam (permanent, hides rust, complicates future work) and fiberglass batts (moisture sponge in a vehicle that flexes).
Ventilation is half the battle
Insulation slows heat transfer; it cannot remove moisture. That is the roof fan's job. A powered fan with a cracked window creates constant gentle airflow that carries humid air out before it finds cold metal.
This is why every Timber kit and conversion is designed around a roof fan from day one rather than treating it as an accessory.
The mistakes we see most
- Stuffing every cavity as tightly as possible — compressed insulation loses R-value.
- Vapor barriers installed like a house. A van is not a house; trapped moisture has nowhere to go. Let the assembly breathe and ventilate instead.
- Skipping the floor because "heat rises." Conduction does not care; your feet will report the difference all winter.
Insulate for the worst night you will actually have, not the expedition you might take someday — then spend the savings on ventilation.
Insulation and wall paneling are included stages in our full conversions, and the kit instructions walk DIY builders through this exact sequence panel by panel.