Should I Use Celotex in My DIY Campervan Build?
Updated: Sep 2
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If you are planning a DIY campervan or van conversion, you will probably come across Celotex, PIR insulation board and other rigid thermal insulation products.
Celotex is inexpensive, widely available and highly effective when used correctly in buildings. But does that mean it is the best insulation for a van?
Not necessarily.
The key issue with campervan insulation is not simply choosing the material with the highest R-value. The insulation needs to work with the shape and construction of the vehicle, fit properly into the available space and deal with the challenges of a metal vehicle shell.
Thermo Liner vs Celotex or Thermal PIR Board
There is a common argument that because R-value increases with insulation thickness, a thick piece of Celotex must be better than a much thinner vehicle-specific insulation.
That comparison isn't quite that simple.
For example, comparing 7mm of Dodo Thermo Liner with 50mm of Celotex based purely on R-value doesn't tell the whole story.
The best insulation is the material that can be installed properly in the location where it is needed.
A rigid board might offer excellent thermal resistance, but if it cannot follow the contours of the van, you may end up cutting it into numerous small sections and leaving gaps between the insulation and the metal panel.
These gaps matter.
For further discussion around using PIR insulation in vans, see this forum discussion about Celotex and PIR insulation and this discussion from the van-dwelling community.
Why Gaps in Van Insulation Matter
A van is very different from a house.
The walls, roof and doors contain ribs, curves, recesses and irregular shapes. Trying to fit thick rigid insulation into these areas can result in multiple joints and gaps.
These areas can reduce the effectiveness of the insulation system and can also create places where moisture and condensation can reach the cold metal shell.
This is one of the reasons we favour flexible closed-cell foam insulation for the metal panels of a van.
Dodo Thermo Liner Pro can follow the contours of the vehicle, allowing much more consistent coverage across curved and irregular panels.
What About Condensation in a Campervan?
Condensation is an important consideration when insulating a van.
The inside of a van is essentially a large metal shell. When warm, humid air meets a cold steel panel, condensation can form.
If rigid insulation boards are installed with gaps behind them, moisture can potentially find its way towards the cold metal.
A closed-cell foam liner installed directly against the vehicle panel helps reduce thermal transfer through the steel and reduces the likelihood of cold exposed areas where condensation can form.
Of course, insulation isn't a replacement for good ventilation. A well-designed campervan should have adequate ventilation to manage humidity and moisture.
Why Use Closed-Cell Foam?
A closed-cell foam liner isn't normally designed to compete with a thick 50mm or 75mm insulation board purely on R-value.
It has a different job.
A product such as Dodo Thermo Liner Pro is designed to:
Reduce thermal transfer through the metal panels
Provide acoustic insulation
Follow the contours of the vehicle
Reduce cold spots across the metal shell
Provide a consistent layer against the panel
Work within the limited space available in a van
Dodo Thermo Liner Pro has a thermal conductivity of approximately 0.034 W/mK, while its flexible construction makes it much easier to install around the complex shapes found inside a vehicle.
What If I Want Better Heat Retention?
If your priority is keeping the van warm, a thin liner alone isn't going to provide the same level of insulation as a much thicker insulation layer.
This is where a multi-layer campervan insulation system makes sense.
Our preferred approach is to use a flexible closed-cell foam liner against the metal panels and then add a thicker insulation layer where there is sufficient cavity space.
For this, we recommend a recycled PET insulation such as Dodo Thermo Fleece.
This provides a thicker layer of thermal insulation without trying to force rigid boards into every available space.
What About Bubble Wrap Insulation?
You will also see bubble foil insulation recommended for campervan conversions.
The shiny foil can look impressive, but reflective foil products rely on an appropriate air gap to provide their reflective insulation effect.
Simply sticking foil or bubble wrap directly against a van's metal panels does not provide the same thermal performance as a properly installed insulation system.
For a useful insulation layer against the vehicle shell, we prefer closed-cell foam designed specifically for vehicle applications.
Can I Use Celotex on the Floor?
This is where the answer can be different.
If you are working to a tight budget and have sufficient space within your floor construction, it may be possible to incorporate a rigid insulation board into the floor.
However, you need to consider the construction carefully.
The floor is also a major source of road noise, tyre noise and low-frequency vibration, so thermal insulation alone doesn't address the acoustic side of the conversion.
For this reason, we generally recommend looking at products specifically designed for campervan floor insulation and sound isolation, such as Dodo Super Liner or Dodo DUO.
These can provide thermal insulation while also helping isolate road noise without unnecessarily increasing the finished floor height.
Should I Use Thermo Liner on the Floor?
Dodo Thermo Liner Pro is designed primarily for use on the walls, roof, doors and other vehicle panels.
It isn't our preferred product for use directly beneath a finished floor.
The floor needs to provide a stable, load-bearing surface, so a dedicated floor insulation product is generally a better solution.
For more information, see our guide to rear floor installations.
So, What's the Best Campervan Insulation?
There isn't one insulation product that is perfect for every part of a van.
The most effective approach is to use different materials for different jobs.
For metal walls and roof:Use a flexible closed-cell foam such as Dodo Thermo Liner Pro to follow the vehicle contours and provide thermal and acoustic insulation.
For larger cavities:Add a thicker recycled PET insulation such as Dodo Thermo Fleece where space allows.
For the floor:Use a product designed specifically for floor insulation and acoustic isolation, such as Dodo Super Liner or Dodo DUO.
For panel vibration:Use dedicated automotive sound deadening such as Dodo DEADN where required.
This approach allows you to build an insulation system around the vehicle rather than trying to make one material do everything.
Is Celotex Wrong for a Van Conversion?
Not necessarily.
Celotex and other PIR boards can have a place in a DIY van conversion, particularly where they can be installed properly, sealed effectively and supported by the surrounding construction.
The problem comes when rigid insulation is used throughout a van simply because it has a high R-value.
If it has to be cut into lots of small pieces, leaves gaps or cannot follow the shape of the vehicle, you may not get the result you expected.
Ultimately, the best campervan insulation is the material that provides good thermal performance and can be installed effectively within the space, construction and budget available.
There are simply too many variables to say that one insulation material is always the answer.
Choosing Insulation for Your Van Conversion
We supply a wide range of campervan insulation, van sound deadening and thermal insulation products specifically suited to vehicle conversions.
From flexible closed-cell foam and recycled PET insulation to dedicated floor insulation and vibration control, we can help you choose the right products for your particular van.
If you're unsure what you need for your conversion, get in touch with us before you buy. Choosing the right combination at the planning stage can save time, space and money later in the build.
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