Why Insulation Is Your Most Important Decision
You can upgrade your solar or swap out your bed. Insulation is different — once walls are up, ripping it out to fix a mistake costs you weeks and thousands. Bad insulation creates condensation that leads to rust and mold. Get this right first.
The Main Insulation Options
Spray Foam (Closed Cell)
The gold standard for vans. Seals metal, acts as vapor barrier, highest R-value per inch.
✓ Adheres to metal
✓ R-6 to R-7 per inch
✗ Hard to DIY perfectly
Polyiso Rigid Board
Best budget option. Cut to fit, tape seams. Pair with spray foam in gaps for best results.
✓ High R-value (R-6.5/in)
✓ Easy DIY
✗ Moisture can sneak behind
3M Thinsulate
Excellent for curves, ribs, and awkward shapes. Doesn't hold moisture — used in premium builds.
✓ Doesn't trap moisture
✓ Easy to cut & install
✗ More expensive per R
Fiberglass Batts
Do NOT use in a van. Holds moisture, supports mold growth, terrible in metal cavity applications.
✗ Mold risk
✗ Not van-appropriate
R-Value: How Much Do You Need?
R-value measures thermal resistance. In a van, you're limited by space — you can't fill 12 inches of fiberglass like a house wall. Aim for these targets:
| Location | Target R-Value | Recommended Material |
|---|---|---|
| Walls (between ribs) | R-8 to R-12 | Polyiso + can foam gaps |
| Ceiling | R-10 to R-14 | Polyiso or Thinsulate |
| Floor | R-6 to R-10 | 1.5" XPS rigid foam |
| Doors | R-5 to R-8 | Thinsulate (flexible) |
| Wheel wells | R-6+ | Spray foam or Thinsulate |
Condensation: The Silent Build Killer
Condensation forms when warm, moist interior air hits cold metal. In a van, you produce moisture constantly — breathing, cooking, showering. Here's the only reliable solution:
- Eliminate all cold metal surfaces — spray foam touching every bare metal surface eliminates thermal bridging
- Ventilate properly — a Maxxair or Fan-Tastic fan running on low at night moves moisture out before it settles
- Use a vapor barrier correctly — or don't use one at all; partial vapor barriers trap moisture
- Monitor humidity — keep a hygrometer; 40–55% RH is ideal
Cost Breakdown
| Item | Standard Transit/Sprinter | Full Skoolie |
|---|---|---|
| Spray foam (2-part kit) | $200–$400 | $500–$900 |
| Polyiso rigid board | $100–$200 | $250–$500 |
| Thinsulate (ceiling/doors) | $150–$300 | $350–$700 |
| Tape, foam, misc | $40–$80 | $80–$150 |
| Total | $490–$980 | $1,180–$2,250 |