Van Insulation: Which Material Should You Choose?
Good van insulation is one of the most important decisions in any conversion. Get it right and your camper stays warm in winter, cool in summer and free from the condensation that leads to mould and rust. Get it wrong and you will feel it every night. The trouble is that no single material is best at everything, so the right choice depends on your vehicle, your climate and your budget. This guide compares the most popular van insulation materials and helps you decide.
What to consider when choosing insulation
Thermal performance (R-value)
Thermal performance is usually measured by R-value, which describes how well a material resists heat transfer: the higher the R-value, the better. Rigid PIR boards are prized for their excellent R-value in a slim, light, affordable panel, whereas purely reflective materials, while useful in some situations, are much less effective in cold conditions. Insulating well, especially in the ceiling, also makes any heating or cooling work less hard and use less energy.
Moisture resistance and mould
Moisture is the number one enemy of a converted van. Poorly managed, it leads to condensation, mould and rust. Some materials handle it far better than others. Sheep's wool can absorb up to 35 per cent of its weight in water while still insulating, which helps regulate humidity. Extruded polystyrene (XPS) offers excellent water resistance, unlike the more porous expanded polystyrene (EPS). Cork combines breathability, natural mould resistance and fire resistance, which makes it particularly well suited to damp climates.
Ease of installation
Fitting insulation into tight, awkwardly shaped spaces can be a challenge. Flexible products like Armaflex are popular for being light and easy to work around curves, though they cost more than options such as XPS. Rigid boards install quickly but need precise cutting to fit. Expanding polyurethane foam can be tricky to control and may even distort the bodywork if applied badly. Sheep's wool, though eco-friendly and free of volatile compounds, can also be fiddly to cut and hold in place.
Cost
Budget is a key factor. Rigid PIR and XPS boards tend to offer the best balance of performance and price, making them the economical, high-value choice. Flexible foams like Armaflex sit in the mid-range, while professionally applied closed-cell spray foam is the most expensive option by some margin. It is worth weighing the upfront cost against the long-term energy savings that better insulation brings.
Environmental impact
The ecological footprint matters more and more. Natural materials such as sheep's wool and cork are often chosen for their low impact, and polyester wool combines light weight and affordability with a smaller footprint than some synthetics. End-of-life recyclability is also worth thinking about in a vehicle built to last for years.
Weight
It is easy to overlook, but the weight of your insulation adds up and has a direct effect on fuel consumption and on how much payload you have left for everything else. Lighter materials such as PIR, Thinsulate and polyester wool help keep the build efficient, whereas denser natural wools weigh more for the same coverage. Balance the thermal gains against the extra kilograms, especially if your loaded weight is already approaching the vehicle's limit.
The most common materials compared
Armaflex (elastomeric foam)
Made from closed-cell elastomeric foam, Armaflex is flexible enough to suit complex, curved surfaces, and its structure stops moisture getting in, which makes it ideal for vans regularly exposed to damp or coastal conditions. Installation is straightforward, but the relatively high price can be a sticking point on a tight budget.
Sheep's wool
Sheep's wool can absorb up to 35 per cent of its weight in water while keeping its insulating properties, and this natural, non-toxic material even improves interior air quality. Its thermal performance, however, is lower than modern synthetics: with an R-value of about 2.63 per 100mm, it often needs more thickness to compete, and it typically costs two to three times as much as glass or mineral wool.
Rigid boards (PIR and XPS)
Rigid boards such as PIR (polyisocyanurate) and XPS (extruded polystyrene) offer a strong balance of thermal performance and cost. PIR leads the way, with an R-value of around 4.16 per 100mm, ahead of XPS at about 3.03 per 100mm. PIR stands out for long-term energy efficiency, while XPS is valued for its water resistance. The catch is that rigid boards need careful, precise cutting to fit curved surfaces, or you risk wasted material and thermal bridges.
Other options (Thinsulate, recycled denim, cork)
Thinsulate is a hydrophobic synthetic wadding with an R-value of about 3.3 per inch. It is easy to install and performs well across a wide temperature range, which makes it a favourite among DIY builders. Recycled denim is eco-friendly but less suitable here, as its poor moisture resistance can encourage mould. Cork is a natural all-rounder, combining breathability, mould resistance and fire resistance, with a useful ability to regulate humidity in damp environments.
Quick comparison table
| Material | R-value (per inch) | Moisture resistance | Installation | Key strengths |
|---|---|---|---|---|
| PIR boards | 5.0-6.5 | Good | Easy | Great performance for the price |
| XPS boards | 5.0-6.5 | Good | Easy | Water-resistant, economical |
| Armaflex | 3.5-4.0 | Excellent | Easy | Flexible, sealed, mould-resistant |
| Sheep's wool | 3.5-3.8 | Excellent | Moderate | Natural, humidity-regulating, non-toxic |
| Thinsulate | ~3.3 | Good | Easy | Thin, light, hydrophobic |
| Spray foam | 6.0-6.5 | Excellent | Difficult | Top thermal performance, airtight seal |
How to choose the right insulation for your van
Match the material to your vehicle. In a compact van, slim rigid PIR boards give excellent thermal performance without stealing interior space. In a larger motorhome, you have room for thicker materials like sheep's wool, or to combine several. Whatever the vehicle, prioritise the ceiling, because warm air rises.
Factor in your climate. In cold or mountainous regions, high R-value materials such as PIR boards or spray foam are ideal for holding heat in winter. In hotter areas, natural materials like wood fibre, cork and hemp slow the transfer of heat, and thermal blinds at the windows reflect the sun to keep the interior comfortable. Across much of the UK and Europe you are dealing with damp winters and the occasional very warm summer, so moisture resistance and ventilation matter as much as raw R-value.
Insulate zone by zone. Start with the ceiling, then move on to the walls and floor. Use rigid boards for large, flat cavities and fix them with suitable fastenings, and switch to flexible materials such as Thinsulate or hemp wool for the fiddly, hard-to-reach spots.
Manage moisture. Fit a vapour barrier between the insulation and the interior, ensure good ventilation with at least one air inlet and one outlet (a roof vent with a fan is excellent), and consider a dehumidifier in very damp conditions. Aerate closed lockers and cupboards regularly so air does not stagnate.
Combine materials. A well-planned mix often beats a single product: rigid boards for the big cavities, loose or flexible wool for the gaps. This lets you play to each material's strengths while keeping the interior temperature stable. It is no surprise that PIR is consistently one of the most popular choices among van builders, precisely because it balances performance, price and ease of fitting so well.
The bottom line
Choosing the right van insulation is about matching the material to your vehicle, your climate and your budget, then fitting it properly. As a rough target, aim for around R-13 in the walls and R-15 in the roof. Whichever material you pick, the fundamentals are the same: seal the surfaces well, fit an effective vapour barrier, guarantee good ventilation and eliminate thermal bridges. Do that, and you will have a camper that stays comfortable whatever the weather outside.
