The Bottom Line
Wheel arch insulation is one of the highest-impact jobs in a van conversion. The difference between a van with untreated wheel arches and one with the three-layer system described here is immediately noticeable — quieter at speed, warmer in winter, and no condensation streaks on the walls.
The materials cost about £70 and the job takes half a day. It is one of the few conversion tasks where the effort-to-reward ratio is genuinely excellent.
My recommendation: Use 6mm closed-cell foam on the front arches and 10mm on the rear. Skip the plywood panelling if you are short on time — automotive carpet directly over the foam gives 90% of the result with less work.
Why Wheel Arches Need Special Attention
Wheel arches are one of the biggest sources of heat loss, road noise, and condensation in a campervan conversion. The metal is thin, it is directly exposed to the outside air and road spray, and the wheel itself generates heat, noise, and vibration that transfers straight into the living space.
A poorly insulated wheel arch means:
- A cold spot on the floor above or beside it
- Road noise at motorway speeds that makes conversation difficult
- Condensation running down the metal and pooling on your floor
- Potential rust if moisture is trapped against bare metal
What Not to Do
Do not use spray foam. Expanding foam in wheel arches creates a moisture trap. The metal sweats, the foam absorbs water, and within 12 months you have rust perforating from the inside. Once spray foam is in a wheel arch, removing it is a nightmare.
Do not leave bare metal. Even if you are planning to cover the wheel arch with plywood or carpet, the metal needs to be treated. Condensation on untreated metal will rust.
Do not use household insulation (fiberglass, mineral wool). It absorbs moisture, sags over time, and provides no sound deadening. Vibration from the wheel will compact it within months.
The Right Materials
Layer 1: Sound Deadening
Butyl rubber sound deadening mats (often sold as "dynamat" or "silent coat") are the foundation. These are self-adhesive sheets about 2mm thick that stick directly to the metal. They dampen vibration and reduce road noise by converting the energy into a small amount of heat.
You do not need to cover 100% of the surface. 40-50% coverage in random patches is enough — the butyl spreads the dampening effect across the panel. A 10-sheet pack (about £20-25 on Amazon) covers both front wheel arches with some left over.
Apply the sheets to clean, dry metal. Roll them firmly with a wallpaper seam roller or the handle of a screwdriver to ensure full adhesion.
Layer 2: Closed-Cell Foam
On top of the butyl, apply closed-cell polyethylene foam (often called "CCF" or "thermawrap"). This is the insulation layer — it stops heat transfer and provides a vapour barrier.
Use 6mm or 10mm thickness. Thicker than that and you start losing too much space in the wheel arch area. The foam is self-adhesive on one side. Stick it directly to the butyl layer, covering the entire wheel arch.
Closed-cell foam does not absorb water. If condensation forms on the metal (it will, even with the butyl), the foam keeps it away from your interior panelling.
Layer 3: Carpet or Panelling
The final layer is cosmetic. You can use automotive carpet (glued to the foam with spray adhesive) or thin plywood (3mm or 4mm) shaped to the arch profile. Plywood gives a cleaner finish and is easier to keep clean, but it takes more time to template and cut.
If you use plywood, seal both sides with a thin coat of PVA or danish oil before fitting. Untreated plywood in a wheel arch area will eventually absorb moisture and rot.
Step-by-Step Installation
1. Clean the Metal
Remove any sound deadening that peeled off from the factory (some vans have basic bitumen pads), degrease with isopropyl alcohol or panel wipe, and let it dry completely. Any grease or dust will prevent the butyl from sticking.
2. Apply Butyl Sheets
Cut the butyl into patches roughly 15cm x 15cm. Apply them randomly across the wheel arch surface, leaving roughly equal gaps. Press firmly. Use a roller to ensure full contact.
Pay special attention to the flat panels on the sides of the arch — these transmit the most vibration.
3. Cut and Fit the Closed-Cell Foam
Measure the wheel arch profile with a piece of cardboard first. Transfer the shape to the foam and cut with a sharp knife or scissors. Fit the foam in sections if needed — a single piece rarely covers the full arch.
Butt the edges together tightly. Do not overlap — overlapping creates lumps that show through the final layer.
4. Apply Vapour Tape
Seal the seams between foam sections with aluminium foil tape. This creates a continuous vapour barrier. Moisture that gets past the foam will hit the butyl and run down to the bottom of the arch, where it can drain out through the factory drain holes.
5. Install the Final Layer
For carpet: spray both the foam and the carpet backing with high-temperature spray adhesive (standard spray adhesive can fail in summer heat). Press into place, working from the centre outwards.
For plywood: screw through the plywood into the metal with self-tapping screws. Pre-drill the plywood to avoid splitting. Countersink the screw heads and cover with a dab of silicone.
6. Check Drain Holes
Every van has factory drain holes at the bottom of the wheel arch. Make sure they are not blocked by insulation or panelling. Blocked drain holes mean standing water inside the arch, which means rust.
Front vs Rear Wheel Arches
Front arches — These take more road spray and transmit more engine noise. The butyl layer is more important here. The arches are also tighter, so use 6mm foam to preserve space.
Rear arches — If the rear of your van has a converted living space, the rear arches are inside the habitation area. They need the same treatment but with thicker foam (10mm) because they are concealed behind cupboards or bed boxes and the extra insulation helps retain heat.
On many panel vans (Ford Transit, VW Crafter, Citroen Relay), the rear wheel arches extend into the load area. These need particular attention because the metal is close to the living space and any gap in the insulation creates a noticeable cold spot.
Common Mistakes
Mistake 1: Insulating only the visible part. The wheel arch extends above and behind the wheel. Insulate the entire metal surface, not just the part you can see from the inside.
Mistake 2: Using too much butyl. More is not better. Butyl adds weight (about 0.5kg per sheet) and provides no thermal insulation. 40-50% coverage is optimal.
Mistake 3: Forgetting the arch above the wheel. The top of the arch, directly above the tyre, gets the most road spray and transmits the most noise. This is the most important area to treat.
Mistake 4: Blocking access to bolts. If your wheel arch has bolts or access points for suspension components, mark their positions on the final layer. Cutting through later to reach a shock absorber bolt is frustrating.
Materials Cost Estimate
| Material | Quantity | Cost |
|---|---|---|
| Butyl sound deadening (40x25cm sheets) | 10 sheets | £22 |
| Closed-cell foam (6mm, 2m²) | 1 roll | £18 |
| Aluminium foil tape (50m) | 1 roll | £6 |
| Automotive carpet (1m x 1.5m) | 1 piece | £15 |
| Spray adhesive (high-temp) | 1 can | £10 |
| Total | £71 |
