How to Choose the Best Insulation for Your Winterised Motorhome – Winter Van Build Part 2

Choosing how you intend to insulate your winterised motorhome or campervan is probably the most important element of any van build or motorhome refurbishment. After an entire season of analysing the thermal insulation in every material and every tiny space in our previous motorhome, we began to research thoroughly to make sure our winterised van build accounted for every weakness we know of. In this article we’re covering the insulation options open to you and delve deeper into our decisions on which insulation route to go down.

How do you choose the best insulation for your winterised campervan? The insulation you choose for your winterised campervan or motorhome will depend on a number of factors including your budget and the time you have available. There are lots of options all with different properties, price points and installation processes – here are the most common van insulation materials:

  • Rockwool
  • Sheep’s wool
  • Celotex (and other brands)
  • Spray foam
  • Foil bubble wrap
  • Fibre glass batts
  • Recycled denim batts 

There are so many articles, blogs and YouTube videos on this topic that we have taken the decision not to reinvent the wheel. We are not physicists or engineers, mechanics or builders. We are (relatively) normal folks who are building a van and we are sharing an insight into our decision making process and not the scientific technicalities and merits of each van insulation option. However, if you are interested (and you probably should be) on the real nitty gritty, check out Gnomad Home who has a really in depth blog on this topic. If you just want a bit or real-world experience to draw on, read on.

Van insulation isn’t rocket science

It really isn’t. But it can be pretty complicated if you start getting into the thermal insulation properties and cost benefit analysis of each option open to you. It is important to note that we firmly believe that a truly winterised motorhome or campervan has specific needs on top of a fair-weather van. The upshot of paying very close attention to the insulation of a vehicle is that it goes both ways, heating and cooling. We are of course razor focused on heating and heat retention. A toasty warm, well winterised van will also be a super cool van in summer with a few additions like air-con – science is clever that way.

How did we decide what to use?

James and I individually looked at the following considerations – and if you’re building your van solo, it’s always an idea to get a different view point, just in case you’ve watched too many YouTube van builds to have any perspective left!

  • Ease of application/installation
  • Cost
  • Time of application/ installation
  • How good is it? i.e. how warm will our van stay?
  • How safe is it? Is it toxic in any way? How fire retardant is it?
  • How versatile is it? Can we use it all over or just in parts?
  • How easy is it to modify if we need to change something?
  • Are there any known issues with using it?

As we’ve said, what you’re not going to find here is any detailed pondering about thermal insulation measurements and numbers – this is as much as we’ll say on the matter. Generally, people talking about thermal insulation will use an R value (resistance value) – this specifically relates to the insulating capability of a material or body. It matters – sure it does. However, when insulating a metal (or plastic composite) box on wheels, we decided that all those factors listed above would collectively have more influence on our insulation decisions than how many fractions of a R, product A would trump product B by. It’s not enough.

It’s important to note that all the products we considered are championed in van builds for various reasons – we didn’t consider polystyrene beans, the masses of free dog hair we have or reclaimed moss. That’s why we could safely discount the marginal differences in R rating of the materials we did consider. That is the reality of it, it’s marginal and there are a lot of other elements of your van build that, if you don’t get right, will render these marginal gains in insulation pointless – gappy windows for example.

condensation in a motorhome
In good news, the condensation drained pretty fast from the gaping holes between the window and the body of this BRAND NEW motorhome.

If you’ve experienced the same issue and you haven’t got a Karcher Window Vac, put down what you’re doing, and immediately get one – you won’t regret it… here’s our complete run down if you want to know more – if you just want to take our word for it, you can get it on Amazon here.

SPOILER ALERT: James is in the ‘what’s the most efficient’ camp and I’m in the ‘what’s the most economical’ camp – somewhere in the middle, we met at choosing spray foam insulation. It was a unanimous decision.

Another Important Note: Taking Advice from Fair Weather Campers

By fair weather campers, we mean people who only take their motorhomes away in moderate weather conditions. A night camping in a half inch of snow in the Brecon Beacons doesn’t constitute deep winter conditions. A border crossing at 1000m does not constitute a high altitude environment and insulating your own summer house doesn’t make you an insulation specialist. Having a YouTube channel on building your own van out of dreamcatchers and pallet wood doesn’t make you a van conversion specialist. It makes you a doer – awesome, just not anyone we’re going to rely 100% on for any advice.

The one thing we have learned from our Winterised ‘journey’ is to question things. Especially when it comes to pseudo science. Listen to people with massive beards; plumbers; people who spend more than 10 days on the road each winter; people who operate cold chambers; and people with a PhD in Physics. Everyone else just offers opinions – take them with a pinch of salt (this includes us although James has a massive beard and is a plumber).

Let’s look at our list:

Ease of Application or Installation

Not a huge consideration for us as James is a very accomplished tradesman. However, something that’s easy to install has often been thoroughly thought through with the user in mind. The wools and fabric insulations are a synch to squish in the walls and cutting them to size is probably as easy as insulation gets. Celotex and other polystyrene materials are a more of a faff – you have to cut it up and measure a lot of stuff and it doesn’t matter how meticulous you are, there are gaps you just can’t get to. It’s actually pretty time consuming. Upside is you can pop back down to B&Q or Travis Perkin when you screw it up to pick up another sheet!

Spray foam. The outsourcing version is simply effortless – drop vehicle off at specialist foam insulation company. Collect it later. All done, just a good chunk lighter in the wallet department. The DIY version is a bit more involved and requires planning and prep work to do a good job. We want to do a good job so that sounds like our kind of solution.

We actually talked at length with the guys who sell DIY spray foam insulation (AB Building Products – they have a lot of info on their website here) because we really didn’t want to take on a job that we were going to mess up. A false economy if you like. We went through the entire process including how to avoid common pitfalls, hints and tips for getting a nice finish and most importantly, how to deal with all the wiring and bits we feared we’d have to set in stone before embarking on what feels like a home chemistry experiment.

What we discovered is that there are two very distinct ways to do a DIY vehicle spray foam insulation job.

  • The right way
  • The ‘don’t read the instructions and just have a go’ way.

They result in two very different outcomes. One is an easy process with a nice result the other is a big ol mess. The choice is yours!

After James committed in a pinky-swear to read the instructions (and follow them) exactly, we decided spray foam was the easiest way for us to insulate the entire van, top to tyres.


Let’s rip off the plaster – if you’re just considering material cost, short of buying a NASA spec patented rocket insulation, spray foam is the most expensive product we considered inch for inch. However I’m an economist and if you start adding in labour and the life expectancy of the materials, the cost of spray foam plummets and becomes more comparable to the other popular insulating materials. Foam boards deteriorate faster than snug fit foam with all the rattling around in a van and batting of all types usually unseats itself in time, sometimes slumping, sometimes contracting or generally moving from where you intend it to be. Spray foam is adhered to your van on all contact surfaces. By my calculations, if you want to ‘set it and forget it’, spray foam insulation wins here.

Time of Application or Installation

This is another question of economics. The preparation of your vehicle should be the same for all insulation projects. Whatever insulation you choose, before you begin, it still needs stripping out and it still needs to be spotless. The temptation is to be a bit lackadaisical if you’re simply shoving a bit of wool in the walls so the spray foam approach appeals to our sense of ‘proper job’.

Installing batting is the fastest option, followed by spray foam, followed by foam boards. You don’t believe us? If you’re doing a proper job with your foam boards, it’ll take longer than it will to spray the van. Measuring, cutting, positioning, trimming, positioning, trimming…. You get the point.

How Good is the Insulation? i.e. How Warm Will Our Van Stay?

We said it was marginal – it is, but a focus on marginal gains is what has won Great Britain a bazillion cycling medals in the Olympics and is the backbone of all motor racing disciplines – the pursuit of marginal gains.

Without boring you with R values – Spray foam wins, every time. Next is foil backed polyiso (foam board) which beats spray foam on cost per inch by a mile of switchbacks.

Here’s how we looked at it. Converting a van for motorhome skiing is a huge investment. All you need to do is look at the price tag on the truly winterised manufacturer-built motorhomes to see that winterising costs. When we’re away, we also want to focus on adventures and not our body temperature. We invest in good clothing, so we are going to do the same with the van.

We also fell into the trap of

Once you know, you can’t unknow

Which leaves us in the position that we know that this is the best product from an R rating perspective and we can’t ignore that given what the purpose of the van is – to motorhome ski.

How safe is it? Is it toxic in any way? How fire retardant is it?

Argh! Back in the day we didn’t know that cucumbers, carpet and water bottles were all carcinogenic. We might have had a sneaking suspicion that breathing in mould wasn’t going to boost your immune system like eating worms does but friends, you really need to pay attention to this stuff if you’re living in a 16m² space with all the windows closed. We have first hand experience of something a little scary in our previous (loaned) motorhome – suspected formaldehyde poisoning – so we’re pretty neurotic about this!

Sheep’s wool is considered to be the most environmentally and health friendly insulation.

How safe is my insulation? We think this is a two pronged topic, both of which answer the question, will it adversely affect my health? Fire retardancy is an obvious one and unless you buy something sketchy from Bob on eBay, or make it yourself from the loo rolls you’ve collected over the years, your insulation material will be compliant with the most up to date fire retardancy regulations. That doesn’t mean your van won’t catch fire, it just means your insulation won’t be a catalyst.

How toxic your insulation is, is an entirely different question to consider, and just because you’re not licking it or using it to filter your drinking water, doesn’t mean it’s not hazardous. We looked at two things. Is the material itself made of a known toxin? Can it become toxic in some way over time? The second question is the one you really want to focus on. Asbestos isn’t toxic until it’s disturbed, sawdust isn’t toxic until you inhale it and the same goes for foam dust and fibreglass.

If you buy the proper material and install it according to manufacturer’s instructions, you’ll be just fine – it’s what happens to it longer term that is the issue. We decided that the wools and battings posed far too much of a mould and mildew threat than we were prepared to take a risk on. With two young puppies on board, the idea of having to deal with any kind of fungal infestation is a huge no. Foam board actually isn’t much better on this front. It leaves gaps – even if you use a spray foam to fill these voids, there will be bits that you cannot get to. That means there’s space for condensation to develop – all it needs is a medium on which to grow and you’ve got yourself an indoor fungi farm – in a hard to reach place. You’ll probably get rust too.

The reason we chose spray foam is if you are diligent and plan properly, ever single nook and cranny can be filled, leaving no space for condensation to accumulate. The foam adheres directly to the van panels (or surface it’s being applied to) and even the tiniest spots can be insulated. No vapour barrier is required, and you can go wild, even insulating behind your door cards.

We’re doing everything we can to limit the obvious health risks we expose ourselves to – with the exception of attaching planks to our feet and pointing downhill from the top of a mountain.

How versatile is it? Can we use it all over or just in parts?

As we’ve just highlighted, you can get in all the gaps with spray foam – using various size hoses, you can feed the foam around the impossible to reach places. You can also insulate to whatever thickness you want – if that means that you’d like slightly more insulation in the sleeping area than around the kitchen, the trigger is in your hands – you can apply as much or as little foam as you wish.

With alternative materials, you’re restricted to the formats it comes in. So what? Well, all vehicles are a bit different and the voids in your van might not be exactly 25mm deep. This means you either have to accommodate the disparity (over or under) in the wall covering you choose. Or, you choose foam and do yourself a made to measure job.

How easy is it to modify if we need to change something?

Modifying the build after insulation was something we were pretty keen to accommodate. You never get things right first time and we just know that something will come up that we have neglected to plan for. This was our primary concern with spray foam but it turns out it was completely unfounded because when we considered it, we realised that it’s more accommodating, not less.

Yes – winding cables and whatnot around batting is easy, same goes for foam board. You can install it first and amend your cabling later. Spray foam can require a little more foresight.

If foresight isn’t your thing, it is, we worked out, completely possible to leave wiring and fittings until after your insulation is complete – simply by carving the foam out. You can cover it over with a spray foam in a can without compromising the integrity of the insulation.

Are there any known draw-backs with using it?

The pros and cons of the various batting solutions and foam boards are well documented – from being fiddly (cutting and fitting foam board) to being expensive (sheep’s wool) – they all have their pros and cons – the biggest draw-back associated with spray foam is that to most people, using a precision nozzle and getting even coving is a new skill. Cutting a bit of wool batting isn’t tricky and even getting it millimetre perfect isn’t critical but there are important processes that need to be executed accurately if you’re going to use spray foam. If you’re not the instruction reading type, spray foam isn’t for you. It involves chemical reactions that need to take place under certain conditions to be effective so if you are a steam in and wing it type, stick to the more forgiving materials!

The 8 Reasons Why We Chose To Insulate Our Vans With DIY Spray Foam

  • It’s easy to achieve a professional standard of insulation
  • The cost is justified in the lifetime of the product
  • It’s relatively fast to apply
  • It provides the best R values of any typical van insulation
  • It’s safe, doesn’t present any health risks and prevents the growth of mould
  • It’s a one-size-fits-all product – we need very little else to supplement the insulation
  • We can modify it as we go
  • It’s tried and tested across a great many applications what we consider a good test of it’s effectiveness in a winter van build.

If you’re interested in following this winterised van build, please join our mailing list and we’ll keep you up to speed with all the information of this and our growing database of aires, campsites, and other motorhome ski travel information.

Related Questions:

How do you prepare a motorhome for winter? Preparing your motorhome with winter largely depends on the base that you’re starting with. Lagging pipework and insulating exposed water tanks is a priority along with ensuring you have appropriate tyres and equipment.

What’s the best water tank insulation? Most motorhomes with external water tanks have bubble wrap insulation foil to protect their tanks from freezing in cold weather. Those travelling to colder climates may choose to upgrade this insulation to Armaflex.


Gobby, opinionated, professional ski bum. Co-founder of the Winterised Project.

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