Updated: Nov 14
No insulation in your van? This is you in winter: ⛄
We all like building snowmen, but I'd rather not be one!
Van conversion insulation is ABSOLUTELY CRITICAL to building a cosy campervan. In this guide we will look atbest the best van insulation on the market. You will learn the theory behind van conversion insulation and installation instructions for van floor insulation (as well as the walls and roof).
I'm Shane, I've been teaching people to convert campervans for many years, I'm the author of The Van Conversion Newsletter, instructor of The Van Conversion Course, and the proud owner of a beautiful self-build campervan called Beans. Now let's jump in a look at the best van insulation!
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Spoiler: This is the best van insulation
We're going to be diving deep into all things insulation in this article - giving you a very thorough understanding. But if you want to cut right to the chase...
I recommend using Polyiso foam board for most of the big exposed areas in your van. It is particularly useful for van floor insulation and for the roof.
Optionally, you can use reflectix as a vapour barrier - but only if you're going to do a kickass job!
Now then, let's dive into some theory followed by installation instructions.
What is insulation?
Insulation is any material that is designed to prevent heat transfer - that is the movement of air from hot to cold. This could be for the purpose of keep the inside of you van cosy in winter (keep the heat in), or to keep it cool in summer (keep the heat out!).
What to consider when choosing van conversion insulation
There are 7 things we should consider when choosing van conversion insulation. They are:
Thermal properties 🥵: How 'insulating' is it?
Ease of installation 🪚: Will it fit where we need it to go?
Health risks 🩺: Will it cause itchiness / chemical off-gassing?
Fire safety 🔥: Is it flammable?
Water absorption 💦: Is it hydrophobic or hydrophilic?
Eco-friendliness 🍃: Was it sustainably made / is it recyclable?
Cost 💰: Everything comes at a price...
Below is a table comparing almost every van conversion insulation on the market. Throughout this guide we will explore the pros and cons of each option and discover the best van insulation.
R-Value (per inch) 🥵
Eco friendly? 🍃
Health Risk? 🩺
Polyiso (Foam board)
Closed-cell Spray foam
3M Thinsulate (Batt)
XPS (Foam board)
EPS (Foam board)
Sheep's Wool (Batt)
Mineral wool (Batt)
Mineral Wool (Loose-fill)
Recycled plastic (Batt)
A Quick Crash Course in Insulation Theory
Before we hop in and look at specific insulating materials, it is important to understand some of the key concepts behind the surprisingly complex world of insulation.
Thermal Conductivity (k-value)
Everything in the known universe has the ability to conduct heat, that is the process by which heat is transferred from the hotter end to the colder end of an object.
Different materials conduct heat at a faster or slower rate depending on their thermal conductivity. A lower thermal conductivity (k-value) results in a lower rate of heat transfer.
A lower thermal conductivity (k-value) will yield the best van insulation.
The formula for thermal insulation takes in four parameters and results in a single value known as the k-value:
Amount of heat transferred
Distance between the two isothermal planes
Area of the surface
Difference in temperature
From the table above, we can see that wool, air, and styrofoam are excellent insulators while the materials at the top (brass, copper, etc.) are very poor insulators.
The key takeaway here is that metals are very poor insulators - heat can pass through them easily, So we need to make sure to to use the best van insulation possible to prevent this!
R-value refers to a material’s ability to resist heat transfer at a certain thickness. It takes the K-value and the thickness of the object into consideration. A higher the R-value will yield the best van insulation.
The formula for R-value is Depth(m) / K-value.
R-value is the most common value we refer to when discussing insulation.
Heat is transferred in 3 ways
Conduction: The transfer of heat by direct contact
Convection: The transfer of heat cause by the motion of fluid or gas
Radiation: Heat that travels through an object in the form of waves / particles (eg. the sun)
In order to get the best van conversion insulation our goal is to reduce all three of these factors as much as possible. Let's explore...
By understanding K-values and R-values we already have a good understanding of how to reduce conduction to give us the best van conversion insulation.
By putting an insulating material on the bare metal of the van, we can slow the transfer of heat by conduction.
It is important that we insulate as much of the van as possible - anywhere left un-insulated or with very poor insulation will act as a thermal bridge. A thermal bridge is an area of an object which has higher thermal conductivity than the surrounding materials; ie. allows heat to pass more easily. It is the path of least resistance and usually where we haven't insulated (eg. wooden support furrings or metal struts).
Most of us know that hot air rises while cold air sinks; this is known as convection. This happens because hot air is less dense than cold air.
Inside the hollow structures of a van (such as inside the metal support frames), this movement of air causes a phenomenon known as air loops. Warm air rises up by convection, then cools and drops as it comes in contact with a cold surface by conduction. This causes a circular/looping movement of air.
Air loops can greatly affect the efficacy of van conversion insulation. To get the best van insulation we need to reduce air loops as much as possible.
In practice, this means filling any cavities in the van with insulation to reduce the effect - this is normally done with insulation batts (discussed later). Make sure you fill the cavity as fully as you can, for air loops can still occur around the insulation if it doesn't fill the entire area [¹]. Be careful though - if you're using insulation batts (eg. mineral wool) make sure you don't 'squish' them and make it dense as this would reduce the R-value! Leave the insulation nice an loose and fluffy.
Another place we typically find convective heat transfer is anywhere air can flow from the inside to the outside of the van. Apart from the obvious fan in the roof (we discuss fan covers later), the air gaps around the side and back van doors allow a large amount of heat transfer to occur.
In order to get the best van insulation possible, we need to cover these air gaps as much as possible! The air gaps around doors are particularly malicious when there is a large temperature difference between the inside and the outside of the van.
There are three ways you can block a draught in a campervan:
Option 1: Furniture
The best way to block air flow through the door gaps is with a physical barrier like furniture. For example in my van, I built benches/storage at the back doors to stop the draught. I noticed a huge difference in van temperature after I built these.
Option 2: Draught excluders
Option 3: Hang up a tapestry
This simple hack can make your campervan a lot warmer! Tapestries usually work best for the back doors of the a van and are very easily installed. The thicker the tapestry, the better the draught exclusion. You can hang a tapestry up using screw hooks.
Radiation heat transfer is a process where heat waves may be absorbed, reflected, or transmitted through a colder body. Hot bodies emit electromagnetic heat waves - eg. the sun. In fact all bodies emit radiant heat according to Planck's law[²].
Some materials are particularly good at preventing radiative heat to pass through (white / reflective materials), while others are very poor (glass / black materials).
Emissivity (e-value) is the value given to an object to describe how susceptible it is to emitting/absorbing heat. The e-value is a scale from 0 to 1; a lower number means a material will absorb less heat.
In order to get the best van insulation possible, one should consider radiative heat transfer.
In practice, this means using a reflective material like Reflectix or Low-E to reduce radiative heat transfer (e-value = 0.03). This is like foil the material they use on spaceships!
We can use Reflectix in three places top get the best van insulation:
1. Window Covers
Because glass has one of the very worst e-values, it is imperative that we cover it up to slowe heat transfer. You can easily make DIY window covers by cutting some Reflectix and attaching some suction cups. As a winter vanlifer, I can tell you first hand the important of window covers! Do it!
2. Fan cover
After you install a fan, you are going to have a hole in the roof that air can pass through; even worse, since hot air rises a lot of it will escape through the fan. To counter this you can make a fan cover using reflectix.
3. Thermal bridges with high e-values
As mentioned before, a thermal bridge is a weak spot in your van, through which heat escapes more readily. This could be exposed metal, or It could be exposed/uninsulated timber frame (furring) that directly touches the outside of the van. The window/fan would also be thermal bridges, but we have discussed them already.
You can cover these high-e thermal bridges with Reflectix to slow heat transfer.
A note on using reflectix:
Reflectix has been the cause of much controversy in van conversion community. A few years ago a plethora of people started using it as insulation even though the R value is practically non-existent. Luckily this carry-on has mostly stopped.
Here is the important thing to know: Reflectix will only reflect heat if there is an air gap!
This means there are only two ways you can use reflectix correctly:
1. Put reflectix directly on thermal bridges (metal/furring) and don't cover it with any wood panelling/ply. The entire van is then the 'air gap' Understandably, this isn't for everyone as it can make your van look a bit gross. But if you want the best van insulation...
2. Put wooden furring on top of reflectix to create an air gap between the reflectix and the wood panelling/ply.
The topic of reflectix lead us nicely onto moisture control - a very very important thing in a campervan. Let's cut straight to the chase...
It is imperative that you keep moisture as low as possible in a campervan. Doing so increases the life of your vehicle, improves the efficacy of some types of insulation, and decreases the chance of health-harming mould/rot.
There are four things you can do to reduce humidity / protect a van from moisture:
1. Keep it warm inside!
The first, and most important way to control moisture in a campervan is to keep it warm inside! Warm air can hold more moisture than cold air, which means that instead of water condensing on the metal of the van, it is held in the air. Mould/rot form when water is present on insulation for too long. If your heater has a thermostat on it, leave it on the lowest setting as much as you can during wet/cold months!
Ensure you have ample ventilation inside! This means having at least 1 fan to allow air to flow.
3. Buy a dehumidifier
I have a dehumidifer in my campervan and it has been a lifesaver during the wet months. It simply sits there, running silently, sucking water out of the air! Simple and effective!
4. Use a vapour barrier
Vapour barriers are another controversial technique used in van conversion insulation. When done right they are highly effective, when done wrong they are detrimental.
A vapour barrier is a material that wraps the van conversion insulation and is designed to prevent moisture from getting into the insulation (preventing mould and improving insulation). Some people choose to use polyethylene sheeting as a vapour barrier, though it is more common to use Reflectix as it can double up as a radiative heat transfer barrier on exposed surfaces.
In theory vapour barriers can be super effective. The problem is that most people will probably not get a 100% seal and this causes a big problem as water in the insulation gets trapped and can't escape! [³]
Only install a vapour barrier if you are absolutely sure you can get a 100% seal. Else, it is better to just let the insulation breath.
Side note: There has been some worry in the van conversion community that installing a vapour barrier can trap moisture at the time of installation. This video address and invalidates that worry.
Types of insulation (Batt vs. Foam Board vs Loose fill vs Spray)
The are many types of insulations used in residential and commercial projects. However for the purpose of van conversion insulation, we can concern ourselves with just four:
Spray foam insulation
Loose fill insulation
Let's explore each of those...
Foam board insulation is an incredibly popular form of van conversion insulation due to its efficacy. It is a rigid panel of insulation that is made of either polystyrene, polyisocyanurate, and polyurethane.
There are three types of foam board insulation:
Polyiso board (PIR)
Foam board is an excellent insulator (has some of the highest R-ratings)
Foam board has good resistance to mold (water resistance)
Foam board is a rigid surface that is excellent at preventing air leaks
Foam board is frequently lined with a reflective foil which lowers its e-value and reduces moisture uptake.
XPS and EPS foam board insulation are an environmental disaster (hydrofluorocarbons)! Polyiso is much better though.
Can be more expensive than other types of insulation
What is the best foam board insulation?
To cut to the chase, polyiso board (PIR) is the best van conversion insulation in this category. It has a very high R-rating, is fire resistant, and a lot better for the environment than XPS. The best known polyiso board manufacturers are Kingspan and Celotex. If you want information on the specific differences between these insulations, check out this video:
Since foam board is probably the best van insulation, I suggest using it as much as possible: on your floor, roof, and walls. You can stick the board insulation to a surface using insulation stick pins (more on insulation installation later!).
Batt insulation (also known as blanket or roll insulation) is fluffy/wooly in texture and usually comes in rolls. The following are all types of batt insulation:
Batt insulation is excellent for filling awkward spaces in your van - you can stuff it places that board insulation couldn't go!
What is the best batt insulation?
3M Thinsulate insulation rolls are the best batt insulations on the market by a long mile. It is very malleable, has a very high R-rating, is water resistant, and poses no health hazard. I highly suggest getting yourself some rolls of the stuff and using it to fill any awkward spaces in your campervan. I recommend using it to fill any air cavities in the van (to prevent air loops). Some people insulate their entire van with Thinsulate (and don't bother with any foam board). However I recommend using mostly foam board and fitting batt insulation in the cavities & smaller places.
Spray foam insulation
Spray foam insulation is polyiso foam in a can. It is an expanding insulation that is rather satisfying to use and quite powerful! As the foam expands, it forms little bubbles/pockets known as 'cells'.
Fits in tight places
Long time to install
Bad for the environment
Closed cell spray foam can cause 'super-heating' which could cause bulging/warping of the metal of your van
There are two types of spray foam insulation...
Open cell spray foam
Lower R-value than closed-cell (R-3.8)
Better for the environment
More breathable than closed-cell (won't trap moisture)
Closed cell spray foam
Highest R-value of most insulations on the market (R-6)
No Bueno for the environment
Instructions on how to use spray foam insulation:
Safety precautions: Spray foam insulation can be a serious health hazard so make sure all your skin is covered and you are wearing a high quality mask/goggles when installing. Spray foam off-gasses for a few days, so ensure good ventilation during installation and for the following days.
Ensure the surface you are spraying is clean, shake the can thoroughly, then spray! Make sure you cover the ground with a tarp as spray foam drips.
Spray foam insulation expands to ~30 times it's liquid size (high expansion foam can expand up to 300X!). So be conservative with your spraying. Apply constant pressure and spray evenly over the surface - don't spray too much.
You can use vertical or horizontal strokes to apply the expanding foam. Here's a video showing the different spraying techniques you can use.
My thoughts: Expanding foam is tricky to use and definitely has its downsides. I recommend sticking to foam board and batts. But if you do choose to use it, I recommend getting a professional to do it for you. The experts should get a clean, airtight finish and you don't have to deal with the mess or off-gassing.
Where Expanding foam can be useful is filling the hard-to-get-at gaps in your van where you cant even fit batt insulation.
Loose fill insulation
Loose-fill insulation is not commonly used in campervans, however it can be a great alternative insulation and is good at filling up little gaps. It is the most environmentally-friendly way to insulate your van!
Loose fill insulation is similar in texture to batt insulation except it is 'loose' rather than coming in rolls. You can simply grab a handful of it.