Sheep's Wool Insulation for Campervan Conversions: Honest Review
Sheep's wool is one of the most popular natural insulation choices for UK van builds. It is sustainable, breathable, and good for the environment — but how does it actually perform in a campervan?
We installed Thermawool (trade name for sheep's wool insulation) in a LWB Renault Master campervan conversion and tested it through a UK winter and summer. Here is the verdict.
What Is Sheep's Wool Insulation?
Sheep's wool insulation is made from low-grade wool that is not suitable for textiles. It is treated with borax (a natural fire retardant) and formed into rolls or batts of various thicknesses.
Common brands in the UK:
- Thermawool (made in Wales, 100% British wool)
- Black Mountain Sheep's Wool
- Bradford Sheep's Wool Insulation
- Second Nature (sheep's wool + recycled polyester blend)
Thermal Performance
| Property | Sheep's Wool | XPS Foam Board | Rockwool |
|---|---|---|---|
| Thermal conductivity (W/mK) | 0.038-0.042 | 0.028-0.032 | 0.036-0.040 |
| R-value per 25mm | ~0.65 | ~0.85 | ~0.70 |
| Density (kg/m³) | 20-35 | 25-40 | 30-60 |
Bottom line: Sheep's wool is about 20-30% less thermally efficient than XPS foam for the same thickness. To match XPS, you need 30mm of wool for every 25mm of XPS.
In practice, this matters less than the numbers suggest because van panels have irregular curves where foam board cannot fit anyway. Wool fills voids that foam leaves as air gaps.
Moisture Handling — The Real Advantage
Sheep's wool's unique property is moisture management. It can absorb up to 30% of its own weight in moisture without feeling wet, and releases that moisture as the air dries out.
What this means in a van:
- Condensation on metal panels is absorbed by the wool rather than dripping onto your woodwork
- The wool buffers humidity swings — the interior feels less clammy
- It does not support mould growth (wool's lanolin is naturally anti-microbial)
- If a leak develops, wool will not rot like wood fibre insulation
Warning: This is NOT a substitute for a vapour barrier. You still need one. Even though wool handles moisture well, the metal panels behind it will rust if moisture reaches them unchecked.
Installation Experience
Pros:
- Cuts easily with scissors or a stanley knife (no scoring and snapping like XPS)
- Holds itself in place behind panel ribs (friction fit) — less reliance on adhesive
- Conforms to curved roof panels and wheel arches without cutting complex shapes
- No itchy fibres (compared to rockwool or fibreglass)
- Pleasant smell — natural wool scent, no synthetic chemical off-gassing
Cons:
- Can sag over time (in vertical panels, add chicken wire or horizontal battens to support it)
- Sheds fibres during cutting (wear a mask — the borax dust is an irritant)
- More expensive than XPS: £12-16/m² for 50mm wool vs £5-8/m² for 25mm XPS
- Takes up more space for the same R-value
Cost Comparison
| Material | Cost per m² (50mm) | R-value (50mm) | Van Coverage |
|---|---|---|---|
| Thermawool 50mm | £14-18 | ~1.3 | 30m² needed for LWB van = £420-540 |
| XPS 25mm (£8/m²) + 25mm | £12-16 | ~1.7 | £360-480 for equivalent coverage |
| Rockwool 50mm | £8-12 | ~1.4 | £240-360 |
Best Use Cases for Sheep's Wool
Ceiling: Excellent. The roof has curves and voids where wool moulds perfectly. Use 50mm.
Side walls: Works well if you have 50mm+ cavity depth. Use 50mm wool plus vapour barrier.
Wheel arches: Perfect. Trim to shape, no cutting geometric patterns.
Floor: NOT recommended. Floor insulation needs compression resistance. XPS or plywood sandwich is better.
Verdict
| Aspect | Rating (1-5) |
|---|---|
| Thermal performance | ★★★☆ |
| Moisture management | ★★★★★ |
| Ease of installation | ★★★★☆ |
| Cost | ★★☆☆☆ |
| Environmental | ★★★★★ |
| Overall for UK van | ★★★★☆ |
Would We Use It Again?
Yes — but only for the ceiling, side walls, and wheel arches. The moisture management advantage is real, and in UK conditions where damp is the number-one killer of self-builds, the extra cost is justified.
Pair it with: A good vapour barrier (500-gauge polythene or Reflectix) on the warm side. Never fit wool without one.
Do not use it for: Floor insulation, or in any area where compression is expected.
Final recommendation: If your budget allows £100-150 extra for insulation, sheep's wool is worth the premium for the peace of mind against damp. If you are on a strict budget, XPS foam with careful vapour barrier work achieves similar results at half the cost.
