How to Choose Campervan Insulation and Calculate Its R-Value

The right insulation is the material that fits the van’s cavities, suits the way you’ll travel and can be installed without gaps or compression. Use this campervan conversion insulation guide to compare R-values at the thickness you can actually fit, rather than choosing by material name alone. For a Low-E radiant barrier to work as intended, leave at least 1 inch (2.5 cm) of air space between it and the van panels.

It’s easy to focus on insulation performance and underestimate the work involved. Cutting and fitting around ribs, wiring and awkward corners takes care. Sound deadening and moisture management also need to be part of the same build.

This guide explains how to assess common insulation options, fit a Low-E radiant barrier, calculate the R-value of your layers and add sound deadening to panels, floors and wheel wells. It also sets out what the installation involves, helping you plan a DIY conversion or make informed choices for a professionally finished campervan.

What Should I Look for in Campervan Insulation?

Choose insulation to suit the available space, how you plan to use the van and the finish you want. Work through these steps before covering the metalwork with lining.

1. Choose wall and ceiling insulation materials

   Measure the wall cavities and ceiling ribs, then compare materials by thickness, fit and thermal properties. Foam board can be cut to fit van cavities and offers thermal and moisture resistance. For context, the guide lists PIR board at 3.40 m²K/W for 75 mm thickness, while XPS foam board is 3.03 at 100 mm. Those figures relate to different thicknesses, so compare like with like.

   Check whether each material suits the spaces around wiring, windows and structural supports. Rigid board can leave gaps in curved sections, while flexible batting can follow them more easily. Consider the available depth: a thicker layer may offer more insulation, but reduce usable space beneath the wall and ceiling linings.

2. Fit rigid boards or Thinsulate

   Cut rigid foam board to fit between ceiling ribs, making a template for each bay rather than assuming the spaces are identical. Test-fit each piece and trim any edges that prevent it sitting neatly. Keep wiring and other components accessible, and don’t compress insulation to force it into a narrow cavity.

   For 3M Thinsulate, plan for the recommended 1-2 inches on walls and ceilings, while allowing it to remain uncompressed. The material is supplied as batting and can be installed with spray adhesive. Press it into place evenly, especially around curves and behind ribs, so the lining does not push it flat.

3. Insulate walls, ceilings and subfloors

   Plan the walls, ceiling and subfloor as connected parts of the same thermal barrier. Start with the largest cavities, then fill smaller openings around ribs and edges with pieces cut to fit. Work around support structures on the ceiling. On the floor, account for how insulation thickness affects the finished floor height and available headroom.

   Before installing plywood wall or ceiling panels, mark the battens and preserve access to wiring and fittings. Fix the plywood to its supports without crushing the insulation behind it. Check panel edges and joins as you work. A careful fit helps prevent exposed gaps and creates a neat, durable finish.

4. Check weight, cost and safety concerns

   Factor in the weight of insulation, battens and plywood: added materials reduce the payload available for passengers and equipment. Insulation itself is not an MOT specification. The vehicle must still meet applicable roadworthiness requirements, and the lining must not obstruct controls, visibility or safety-related components.

   The amount required in the UK depends on the material, thickness, area covered and whether you install it yourself. For fire safety, review the material’s stated properties before enclosing it, and keep heat-producing equipment clear of unsuitable insulation. Ventilate during installation and plan airflow in the finished van to help limit condensation.

Low-E reflective radiant barrier installation

Use a reflective layer as part of a considered insulation build, not as a replacement for every other material. Air space, sealed joins and moisture control all affect how the layers work together.

1. Plan thermal breaks and radiant barriers

   Map the metal ribs and panels before adding layers. Thermal breaks interrupt heat transfer through these conductive parts, while a radiant barrier reflects radiant heat across an air space. Reflectix has an R-value of about 1.0 for the whole product, not per inch, so treat it as a supplementary layer rather than relying on it alone.

   Plan the insulation and reflective material around the van’s ribs, wiring and intended lining. A reflective surface pressed directly against a panel lacks the air space needed to work as a radiant barrier. The barrier reflects radiant heat, while other insulation layers resist heat flow through the structure.

2. Install the Low-E reflective barrier

   Measure each section, then cut Low-E to suit the area before fixing it in place. The material is described as 7/32 inch thick, with aluminium foil on both sides, and supplied in rolls six feet wide. Leave at least 1.0 inch (2.5 cm) of air space between reflective bubble insulation and the van panels.

   Where Low-E sits over Thinsulate, maintain an air gap of about 1/2 inch or more between the layers. This is a separate gap from the space behind reflective bubble insulation. Avoid crushing the batting or bridging the planned gap with adhesive, fixings or offcuts.

3. Decide whether to add a plastic vapour barrier only after planning how to seal every edge and opening. A barrier can help limit moisture from cooking and breathing reaching the insulation, but it should be fitted only if you can seal it completely. An incomplete layer may trap moisture rather than control its movement.

   Seal joins and penetrations consistently, including around windows, doors and electric cables. Check every seam before fitting the interior lining, when access is still straightforward. Ventilation also matters: keep air moving in the finished campervan to help manage condensation on cooler surfaces.

4. Keep spray foam separate from the reflective layer’s air gap. Spray foam expands to fill gaps and crevices, which can help seal air leaks, but using it near the barrier can close the space needed for radiant performance. Apply it only where it suits the cavity, and avoid excess that could distort adjacent layers.

   Before covering the build, inspect the full sequence: van panel, air space, insulation and reflective barrier. Check the Low-E faces remain clean, the gap stays open and seams are sealed where required. If you’re planning a tailored campervan conversion, this layer-by-layer approach helps define the finish before the lining goes in.

How do you calculate the R-value?

Use this campervan conversion insulation guide to compare thermal resistance at the thickness your van can accommodate. Keep units consistent, then allow for gaps and thermal bridges in the finished build.

1. Compare R-values and K-values

   Start with the insulation’s stated R-value and thickness. R-value measures resistance to heat flow: a higher figure means greater resistance for that layer. For example, the guide lists PIR board at 4.16 m²K/W for 100 mm thickness, with a K-value of 0.024 W/mK.

   K-value, also called thermal conductivity, describes how readily heat passes through a material. A lower K-value indicates less heat conduction. Compare products at matching thicknesses and units; don’t compare a per-inch figure directly with an R-value per 100 mm.

2. Check Thinsulate rating and thickness

   Measure the cavity depth before selecting 3M Thinsulate. Its stated R-value is 5.45 per inch, so multiply that rating by the installed thickness in inches to estimate the layer’s R-value. For example, at 1 inch, the stated rating is 5.45; at 2 inches, it is 10.9.

   Thinsulate must remain uncompressed to work effectively. The guide recommends 1-2 inches for campervan walls and ceilings, but the available cavity determines what fits without bulging the lining. Keep thickness units consistent throughout your calculation.

3. Calculate each layer separately, then add the R-values of layers arranged in sequence. Combine insulation values only when the figures use compatible units and match the installed thickness. Don’t treat an air gap or reflective layer as equivalent to a solid insulation layer.

   How much insulation do campervan walls, roof and floor need? There is no single thickness for every van. Cavity depth, material performance, headroom and floor height all shape what is practical. Use each product’s rating for the thickness that the area can accommodate.

4. Inspect ribs, doors, windows and corners before fitting the final lining. Metal ribs can conduct heat around insulation, creating thermal bridges. Cut pieces closely, fill accessible gaps and use thermal breaks to interrupt this path. Around openings, fit insulation carefully without blocking moving parts or creating draught routes.

   How can you insulate around ribs, doors, windows and awkward spaces without thermal bridges? Measure each recess, cut insulation to fit and cover exposed metal where the build allows. Seal draught routes around openings while keeping doors, windows and electric components unobstructed.

5. Allow for real-world conditions when assessing your calculation. Adhesive, compressed insulation, exposed metal and poorly fitted joins can reduce a layer’s theoretical performance. Assess the complete wall, roof and floor assembly rather than relying on one headline figure.

   Moisture also affects comfort: warm, humid air meeting a cold surface can cause condensation. Plan ventilation alongside insulation, and avoid trapping damp behind closed linings. A campervan conversion insulation guide should account for the whole build-up, including the quality of the fit and changing UK weather.

Sound deadening for van panels, floors and wheel wells

Prepare by clearing the floor and panels, then clean and dry each surface before fitting anything. Apply sound deadening first, followed by insulation and the subfloor, wall and roof lining.

1. Apply sound deadening to van panels

   Cut 80-mil sound-deadening material to fit flat sections of each panel. Cover about 25% of each panel rather than lining the entire surface; this reduces panel vibration without adding material everywhere. Press each piece firmly onto clean metal, avoiding ribs and areas needed for wiring or fittings.

   Work methodically around wheel wells and larger vibrating panels, making sure the material follows the shape without loose edges. Sound deadening and thermal insulation do different jobs: one dampens vibration, while the other slows heat transfer. Keep window mechanisms and door openings clear as you prepare the surfaces.

2. Use reflective bubble wrap on the floor

   Use reflective bubble wrap only as part of a layered floor build, not as the sole insulation material. Reflectix is less effective on its own than other insulation options. A reflective layer needs an air space to work as a radiant barrier, so don’t trap it tightly between the van floor and another layer.

   Cut around floor ribs and mounting points, then keep joins neat and secure. A heater can warm the cabin, but it doesn’t replace insulation beneath the floor. Check that the finished layers are stable underfoot and don’t interfere with doors or floor-mounted fittings.

3. Choose a floor insulation board to suit the available height. The guide lists XPS foam board at an R-value of 3.03 for 100 mm thickness, while EPS is listed at 2.77 for the same thickness. Compare ratings at the thickness your floor can accommodate, rather than choosing by the material name alone.

   As an example of another build approach, 25 mm Celotex has been used beneath a campervan floor. Fit boards between battens, cut around wheel arches and secure the subfloor above them. Keep the board supported and avoid leaving large open gaps between pieces.

4. Plan floor, wall and roof insulation as one sequence, adapting each layer to its cavity. The floor needs a firm, level base; walls must fit around structural ribs; roof layers need clearance for fittings. Measure each surface before cutting, and make sure insulation won’t obstruct electric cables or access points.

   Fit the subfloor soon after laying fragile floor insulation to reduce the risk of damage during later work. At the walls and roof, trim around ribs and openings rather than forcing oversized pieces into place. A neat fit supports the lining and helps limit draughts at joins.

5. Follow a clear preparation and fitting order: remove existing floor coverings, clean and dry the metal, apply sound deadening, then fit insulation and the subfloor. Measure each panel and wheel well, cut pieces to shape and test-fit them before securing or covering them.

   Finish by checking that the floor is even, window and door mechanisms move freely, and no insulation covers wiring or fittings. Inspect the roof and wall joins before installing the final lining. These checks can help prevent having to reopen finished panels to correct a misplaced cut or loose edge.

How difficult campervan insulation can be

Insulation is manageable as a DIY project, but expect careful measuring, awkward access and plenty of fitting. The hardest part is usually achieving consistent coverage around the van’s structure without rushing the finish.

1. Prepare the interior before opening insulation packs. Remove trim and floor coverings where needed, then clean and dry each metal surface. Mark ribs, wiring, windows and fixing points so they remain visible during the work. Ventilate the van during installation, particularly when using adhesives, and keep the workspace clear as you move between the walls, roof and floor.
2. Allow time for accurate measuring and repeated test-fitting. Curved panels, narrow roof spaces and wheel arches rarely suit one-size cuts. Make card templates, label each piece by location, then trim the insulation gradually. This reduces waste and helps prevent compressed sections or gaps that are hard to reach after lining.
3. Break the job into stages rather than trying to insulate the whole van at once. A reported campervan insulation project took about 2 days, with 6-7 hours of work each day, yet the work took three times longer than expected. Treat that as a reminder to leave room for cutting, adhesive application, clean-up and unexpected adjustments.
4. Check each material’s fitting requirements before choosing your method. Flexible batting can follow curved surfaces, while rigid foam board needs careful shaping around ribs and corners. Spray foam expands into gaps, but overusing it can make the job messy. Keep ventilation in mind during application, and allow the material and adhesive to settle as directed before covering them.
5. Inspect the finished layers before installing interior panels. Look for bare metal, loose edges and insulation pushed flat behind battens. Check that doors, windows and electric fittings still operate freely. In summer, a well-planned thermal layer can help limit heat entering through the van body. In colder weather, attention to gaps and contact points matters just as much.
6. Decide which tasks suit your tools, time and confidence. Straightforward areas may be within reach for a careful DIY builder, whilst complex layouts or extensive lining work demand more planning and precision. If you’d rather have the whole build coordinated, plan your campervan conversion around your travel needs and preferred finish.

Route 300 Campers: VW T7 Campervans

Route 300 Campers can help when you’re weighing up a self-build against a professionally planned campervan conversion. Its VW T7 Campervans and Used Campervans suit buyers looking for a ready-to-drive base, while Full Campervan Conversions are an option if you have a van and want the interior planned around your travel needs.

Insulation choices affect the space available for furniture, storage and everyday living, so it helps to consider them alongside the full layout. Route 300 Campers also offers Campervan Kitchen Units, which can form part of a practical interior design. Discuss how you expect to use the van, from weekend trips to longer journeys, and what you want the finished space to include.

For a tailored conversation about your campervan plans, contact Route 300 Campers or visit route300campers.co.uk.

Plan the next stage of your campervan build

Use this campervan conversion insulation guide as a starting point, then consider how you want your van to work on the road. Sketch your layout before fixing the interior, noting where you need storage, sleeping space and room to move. These choices can shape where the insulation and lining fit, helping the finished space feel considered and practical for your travels.

If you’d like a hand turning those ideas into a build plan, contact Route 300 Campers today to discuss your plans. Bring your rough layout and the journeys you have in mind; they’re a useful starting point for shaping a campervan around the way you want to travel. Your next adventure begins with a design that feels right for you.

Frequently Asked Questions

Vapour barrier or not?

Choose a vapour-control layer as part of the complete wall or roof design, rather than adding a sheet by default. Consider the insulation type, interior lining and how you’ll use the van, including for cooking and overnight stays. Don’t assemble layers without understanding how the materials handle moisture movement. Planning the build-up makes it easier to decide whether a separate membrane belongs in your conversion.

What is a thermal bridge?

A thermal bridge is a part of the structure that transfers heat more readily than the insulation around it. In a van, metal ribs and frames can create these paths. Map the metal supports before lining, then check junctions around door frames, roof supports and furniture fixings to spot likely problem areas. Pay attention to these locations when planning the interior, even if the main insulation fits neatly.

What insulation materials are best for a UK campervan conversion?

No single material suits every van. Base your choice on the shape of each cavity, the planned lining and the space available for insulation. Consider how easily you can cut and position it, and whether you’ll need future access to wiring or fittings. A conversion with curved walls and frequent access needs may call for different materials from a build with broad, regular cavities.

What are the R-values and thermal performance of common campervan insulation materials?

For a fresh comparison, open-cell spray foam is listed at R-3.8, whilst closed-cell spray foam is R-6. Rockwool is R-4.3 per inch, and fibreglass insulation is R-3.2 per inch. These figures use different material types, so compare them only at the stated thickness and unit. Product data for the exact material you intend to fit helps make the comparison more useful.

How to prevent condensation, damp and mould in an insulated campervan?

Watch for places where moisture can linger out of sight, such as beneath mattresses, inside storage lockers and behind removable cushions. After a wet journey, dry damp bedding and luggage before putting them away. Check hidden surfaces during regular cleaning, particularly after trips in cold or rainy weather. Addressing small damp patches early can help prevent a larger interior problem.

Should you use a vapour barrier in a campervan conversion?

A vapour barrier can be appropriate, but its role depends on the materials and layers in your planned conversion. Treat it as one part of the wall or roof assembly, not a stand-alone fix. Consider whether other layers already restrict moisture movement: adding materials without assessing the whole build-up can complicate how the assembly dries. Plan the sequence before installing the interior lining.

Is sheep wool, recycled plastic, PIR, XPS or elastomeric foam best for a campervan?

Choose insulation for the requirements of each area, not by a universal ranking. Rigid PIR or XPS may suit cavities where board can be cut to shape; flexible materials may suit less regular spaces. Compare the product’s stated properties, how it fits and how it sits behind the finish. For elastomeric foam, assess the specific product information rather than assuming every foam type performs alike.

How much does campervan insulation cost in the UK?

UK costs depend on the material, thickness, area covered and whether you install it yourself.