There's no single "best" van insulation — there's a best insulation for your climate, budget, and how much wall thickness you're willing to give up. Here's an honest comparison instead of a single product recommendation.
R-Value Comparison by Material
| Material | R-Value per inch | Moisture Resistant? | Relative Cost |
|---|---|---|---|
| Polyiso rigid foam | R-6.0 | Yes | $$ |
| XPS rigid foam | R-5.0 | Yes | $ |
| Closed-cell spray foam | R-6.0–6.5 | Yes (fully sealed) | $$$ |
| Sheep's wool | R-3.5–3.8 | Moderate (wicks, dries) | $$$ |
| Thinsulate (mineral wool blend) | R-3.3–3.5 | Yes | $$$ |
| Reflectix (radiant barrier only) | R-1 (with air gap) | Yes | $ |
| Fiberglass batts | R-3.1–3.4 | No — avoid in vans | $ |
Fiberglass is the one material worth actively avoiding. It holds moisture instead of shedding it, which in a van's inevitable condensation environment leads to mold growth inside your walls where you can't see it.
Rigid Foam (Polyiso / XPS)
Best for flat surfaces — floor and large wall panels — where you can cut clean pieces. Highest R-value per inch of any common option, fully moisture-proof, and the cheapest way to hit a high R-value. The downside: it doesn't conform to curved sheet metal ribs or complex cavities, leaving gaps unless you combine it with a second material.
Best for: floor, ceiling flat sections, budget builds prioritizing R-value per dollar.
Closed-Cell Spray Foam
Highest air-seal quality of any option — it expands into every gap and cavity, eliminating the thermal bridging that plagues rigid foam installs. Also adds structural rigidity to wall panels. The tradeoffs: professional installation is expensive, DIY kits are messy and inconsistent, and it's permanent — there's no removing it later if you need to access wiring.
Best for: builders prioritizing maximum thermal performance and air sealing, willing to pay for it, doing wiring runs before spraying.
Sheep's Wool and Thinsulate
Both conform easily to curved panels and ribs, are non-toxic to work with (no fiberglass itch or foam off-gassing), and — unlike fiberglass — actually manage moisture instead of trapping it. Sheep's wool absorbs moisture and releases it as conditions change; Thinsulate resists it more directly. Lower R-value per inch means you need more thickness for the same performance, which matters in a van where every inch of wall cavity is limited.
Best for: builders prioritizing ease of install around curves, non-toxic materials, and moisture management over maximum R-value.
Reflectix: Useful, But Not a Standalone Insulator
Reflectix only works as a radiant barrier when installed with an air gap on both sides — glued directly to metal, it does almost nothing. It's commonly oversold as a primary insulation layer. Use it as a supplementary radiant barrier against direct summer roof heat, not as your only insulation material.
What Most Modern Builds Actually Do
The most common current approach combines methods by zone: rigid foam (polyiso) on the floor and flat ceiling sections for maximum R-value where it's easy to cut clean, and Thinsulate or sheep's wool in the wall cavities and ribs where flexibility matters more than R-value per inch. This hybrid approach balances thermal performance, moisture safety, and buildability better than committing to one material everywhere.
Frequently Asked Questions
Is spray foam worth it for a van conversion? It offers the best air-seal and thermal performance, but at a real cost and installation difficulty premium, and it's permanent. Worth it if budget allows and you're confident in your wiring layout before spraying.
What insulation should I avoid in a van? Fiberglass batts — they hold moisture rather than shedding it, creating hidden mold risk in a van's condensation-prone environment.
Do I need a vapor barrier with van insulation? It depends on the material and climate — closed-cell foam and rigid foam are effectively their own vapor barrier when sealed well; wool-based insulation is more forgiving of some vapor movement by design. Research your specific climate before deciding.