Van insulation... welcome to the most controversial topic since the creation of #Vanlife! After years of passionate debate, Internet experts still can't agree on the best insulation for DIY van conversions. Let's hit pause on the emotional debate and do it our way: with theoretical analysis and real-life follow up.
Table Of Content
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1- Jumping to Conclusion
We’re not fans of shortcuts and hasty decisions, but there you have it. After 2 winters of full-time vanlife at temperatures as low as -22F (-30°C) and up to 95F (35°C), we recommend insulating your van with:
Thinsulate
We personally used Thinsulate in our van. It has kept us warm, no mold, no bugs, since 2017. It’s SO easy to work with, and there are no chemicals added (as fire retardant or bug prevention). We and our van love it.
(Shipping to USA and Canada. USA orders are tax free and ship from USA warehouse. Canadian orders are subject to taxes and ship from Canadian warehouse.)
That being said: knowledge is power! Make your own conclusion about van conversion insulation by reading the whole thing below… 🙂
2- Theory
2.1- Heat Transfer 101
The goal of adding insulation is to combat heat loss. Heat loss happens because of heat transfer (a.k.a. heat flow). Heat is always transferred from warm to cool and continues as long as there is a temperature difference; a larger temperature difference means more heat transfer potential. There are 3 heat transfer mechanisms: Conduction, Radiation & Convection.
Conduction
- Conduction is heat transfer through a material.
Examples:
- A pot handle (see picture above!)
- A spoon in a hot cup of tea
- A metal van surface getting hot inside the cargo area on a sunny day
HOW:
Energy is stored in the vibration of atoms. More heat = more energy = more vibrations. The collision of atoms between each other transfers heat.
Insulating for conduction:
The more dense a material, the closer the atoms are from each other and the more they transfer energy to their adjacent atoms (by physically colliding with each other). Therefore:
Less dense materials are a better insulator for conduction.
Radiation
- Radiation is heat transfer through electromagnetic waves.
Examples:
- The sun
- A Mr. Heater Buddy (there is some convection too but it's mainly radiant)
- A van dash getting hot when exposed to the sun
HOW:
Any hot (or warm) object radiates electromagnetic waves and can heat up other objects at distance (and therefore lose heat themselves). Energy is transferred through the electromagnetic waves, therefore, thermal radiation can happen through vacuum (without the presence of matter).
Insulating for radiation:
A white shiny surface is poor at absorbing and radiating heat. It is, therefore, a good radiant barrier.
Convection
- Convection is heat transfer through fluid (or gas) movement.
Examples:
- Hot air rising above an intense heat source (i.e. electric heater); Cold water falling towards the bottom of a lake
- A vehicle ventilation system (hot/cold air travels with the air being pushed by the fan)
HOW:
Heat is “transported” from one part of a fluid (or gas) to another by the bulk movement of the fluid itself. Hot regions are less dense, so they tend to rise and are replaced by cooler fluid from above.
Insulating for Convection:
Insulating hollow structure (i.e. frames) and eliminating air gaps minimizes air movement and reduces heat loss through convection.
While heat transfer can be separated in to 3 separate mechanisms, heat loss normally implies all 3 of them together. For example, a hot cup of coffee:
- Heat is transferred from the liquid to the cup surfaces (conduction + convection from the circulation),
- From the cup to the air and objects nearby (convection+radiation),
- From the cup to the cold table underneath (conduction),
- Blowing on coffee to cool it down (convection).
- (Heat is also lost through evaporation -change of phase-, but that’s out of our scope).
2.2- R-Value
Insulation materials are good at resisting heat flow. To quantify how good an insulating material is and to allow easy comparisons between them, a neat dude came up with R-value.
R-VALUE
R-value denotes the capacity of an insulating material to resist heat flow. The higher the R-value, the greater the insulating power. It is normally noted (for example) “6.5 per inch“, which means applying one inch thickness of the material will provide 6.5 R-value; applying two inches will provide 13.0 R-value; and so on. R-value takes into account all three heat transfer mechanisms (conduction, radiation, convection). R-value is determined with the ASTM C518 test (“Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus”).
2.3- Condensation and Moisture Control
Vapor Barrier or not?
The purpose of a vapor barrier is to prevent moist air (from inside the van) from migrating towards cold surfaces. The idea is that moist air from respiration, cooking, drying gear, etc. won’t reach cold surfaces, thereby eliminating condensation issues. However, if, for any reason, moist air makes its way past the vapor barrier, it would be very hard to dry that moist air because it would be sandwiched between two vapor barrier layers (remember that metal is a vapor barrier too).
Even if one could achieve the perfect vapor barrier (which is unlikely, sorry), there are paths for outside air (charged with moisture) to infiltrate, and there are potential leak points as well:
Therefore, we believe that moist air will inevitably come in contact with cold structure, so our approach is to let the insulation layers “breathe” (no vapor barrier).
Condensation and moisture is quite complex, there is much more to talk about… we think this article should help you understand the phenomenon and help you make a better informed decision about your insulation:
2.4- Thermal Bridges
A thermal bridge is a path of least resistance for heat transfer. In other words, it’s a path for heat to “cheat” your insulation and find a way around it. It normally occurs via conduction through a dense material (such as metal).
Take for example the following picture. We added Thinsulate pretty much everywhere, except on the frames and pillars where we will attach our structure (cabinets, etc.). All the exposed metal is considered a thermal bridge, and heat will flow through it around the Thinsulate.
To mitigate the thermal bridges, a thermal break is added. We added LOW-E (EZ-COOL) since it’s pretty resistant to compression (applied by the structure attached to the van’s frames).
That’s important, especially if you’re using 80/20 aluminum extrusions for your build (structure, cabinets, etc.). Indeed, attaching the 80/20 aluminum directly to the van metal creates excellent thermal bridges; as a result, the 80/20 inside your van will be almost as cold as the van metal!
2.5- Air Loops
Hot air is less dense, so it tends to rise and be replaced by cooler air from above. That’s called an air loop and it’s a phenomenon that happens in non-insulated, hollow structures, like in the frames and pillars. So, to the question: “Is it worth shoving insulation inside frames knowing heat will find a way around (thermal bridges)?” We think it’s worth it. The total heat loss of your van is the sum of all the small pieces and bits… It all adds up!
3- Van Insulation Materials
At this point, we’re still on our quest to find THE BEST van insulation material… But in order to find out, let’s review our different options:
Thinsulate
- R-Value: 3.3 per inch.
PROS
- Very easy to install
- Hydrophobic (doesn't retain moisture)
- Doesn't off-gas
- Doesn't lose fibers and not itchy
- Good noise insulation
- Can be stuffed in hard-to-reach places
CONS
- More expensive
Bottom line: it’s a popular tried-and-true product that gives an added value to higher-end builds.
Polyiso Rigid Board
- R-Value: 5.6 per inch at 75F, 5.0 per inch at 15F.
PROS
- Impermeable to water vapor.
CONS
- R-value decreases substantially at cold temperature.
- Creates air gaps on funky surfaces (which is mostly the case in vans) = water traps.
XPS Rigid Board
- R-Value: 5.0 per inch at 75F, 6.0 per inch at 15F.
PROS
- Provides more reliable thermal performance than Polyiso.
- Impermeable to water vapor.
CONS
- Creates air gaps on funky surfaces (which is mostly the case in vans) = water traps.
- Maximum service temperature: 165F. (a darkly painted roof will get hotter than that in the sun! source: phys.org)
Spray Foam
- R-Value: 6.5 per inch.
PROS
- Conforms to curved surfaces.
- Impermeable to water vapor.
CONS
- Can distort the van panels if applied in thick layers.
- Messy to apply.
- Will block mechanism if no precautions are taken (e.g. doors).
- Some body shops won't do repairs if spray foam was applied.
Rockwool
- R-Value: 3.0 per inch.
PROS
- Easy to install
- Hydrophobic (doesn't retain moisture)
- Doesn't off-gas
CONS
- Itchy
- Can release fibers
Reflectix
- R-Value: 1.0 per inch.
Once upon a time, someone decided to insulate his van with Reflectix and blogged about it. Then everyone started using it.
By now, we know Reflectix is a very poor insulator. And on top of that, it requires an air gap in order to be effective.
It’s a good option to make your own window covers (to reflect the sun), but we prefer LOW-E as it is more resistant to tear and doesn’t have that annoying foil noise.
Low-E (EZ-Cool)
- R-Value: ?
PROS
- No foil noise
- Resistant to pressure (when inserted between van and structure)
Low-E insulation (formerly EZ-COOL) is sold as a “radiant-barrier”. It doesn’t have much R-Value, but it’s convenient to use as a thermal break and for insulated window covers.
From Heros to Zeros:
Recycled Denim
- R-Value: 3.5 per inch.
Why we don't recommend it
It’s hydrophilic: it absorbs and retains moisture. People sometimes attempt to enclose it in garbage bags only to find out later that the bags are torn and the insulation is soaked or moldy.
Fiberglass
- R-Value: 3.2 per inch.
Why we don't recommend it
It’s hydrophilic: it absorbs and retains moisture. People sometimes attempt to enclose it in garbage bags only to find out later that the bags are torn and the insulation is soaked or moldy.
Lizard Skin and other insulating Paint
- R-Value: Negligible
Why we don't recommend it
By now we know that efficient insulation materials are low-density. A coat of paint is everything except low density…
The manufacturers don’t provide any data (i.e. R-value, etc.) to backup their claims; there’s probably a good reason why (it would be fairly easy to test and publish data).
According to this Scientific American article, the EPA does not recommend insulating paint: “We haven’t seen any independent studies that can verify their insulating qualities”. They noted some heat gain reduction on surfaces directly exposed to sun only, and that “the reflectivity of the painted surfaces decline considerably with time”. It’s all about reflectivity, not insulation capacity. Are you really gonna paint the exterior or your van with insulating paint..?
Until independent studies show a benefit of insulating paint through standardized test, save your money and your time.
4- Our Insulation Strategy
Going from theory to real-life implies making compromises; there is no perfect solution! The best vanlife insulation is not just about R-Value, it’s also about:
- Ease of installation for the average DIYer
- Risk of messing things up (i.e. warped van panels)
- Condensation and moisture control
- Conformity to curved and uneven surfaces
- Material properties (i.e. maximum temperature, resistance to pressure)
With that in mind, here is how we insulated our campervan:
4.1- Floor
- XPS RIGID BOARD
To be efficient, any compressible insulation material (thinsulate, wool, etc.) must be fully expanded. As a result, they’re not ideal for floor insulation. On the other hand, XPS is an excellent insulator, provides a solid and flat foundation for our floor, is quite cheap, and is readily available at your local hardware store.
So, does it work in real-life? Definitely! We installed our Webasto so it blows hot air in our living space near and parallel to our floor; as a result, the floor is nice and warm, even in sub-freezing temperatures. But don’t get us wrong: the farther you go from the Webasto, the colder the floor gets. Cold air falls, remember? So even a perfectly insulated floor won’t be nice and warm all over unless it’s heated somehow. No, we don’t think a radiant heated floor is necessary (but could be a nice luxury); a pair of slippers is just fine and much more energy efficient!
We chose XPS Rigid Board C-200 to insulate our floor. The C-200 is rated 20PSI capable; human footprint = 16 PSI.
Here are our layers from bottom-up:
- 1/2″ thick XPS (to fill the corrugations)
- 1″ thick XPS
- MLV -not shown in the picture- (noise insulation, but we’d skip that layer if we had to start over)
- 1/2″ thick Plywood
- Vinyl Flooring -not shown in the picture-
We documented EVERYTHING about our floor installation here (insulation, sealing, bonding, plywood, vinyl, etc.):
4.2- Walls, Ceiling, Overhead cabin & Sliding Door
- THINSULATE
Installing Thinsulate insulation in a DIY conversion is a piece of cake: there’s no mess, no risk of messing things up, it’s not permanent, and it’s easy to work with. You’ll be all done in a weekend. Here is how it goes:
- Cut Thinsulate to size (using tailor scissors)
- Apply 3M 90 spray adhesive to the van wall and on the white face of the Thinsulate
- Wait 30-60 seconds for the adhesive to become tacky
- Press the Thinsulate against the wall
- That’s all!
How does it perform in real-life? Since we moved full-time in our van (2017), we’ve had everything between -22F (-30°C) and +95F (+35°C), and we’re in a good position to say it’s a tried-and-true van insulation material. If we had to build another van, we’d use Thinsulate insulation again without any hesitation.
We documented EVERYTHING about the installation of our Thinsulate insulation (walls, ceiling, overhead cabin storage, sliding door, etc.) in the following article. We also have a calculator to help you find out how much insulation to purchase:
- LOW-E
We covered all the remaining exposed metal and about 50% of Thinsulate surfaces with LOW-E insulation; this is to create thermal breaks and add some radiant barrier. We didn’t completely cover the Thinsulate in order to let it “breathe” (the LOW-E acts as a vapor barrier). As usual, we documented the whole thing:
4.3- Windows
- DIY Insulated Window Covers
You can spend a lot of money and time on the best insulation, but remember that glass is an excellent heat conductor (in other words, a horrible insulator). You can make cheap & dirty Reflectix covers to reflect the sun in summer, but if you are skiers like us, you will want something that performs better… To minimize heat loss during winter, we made insulated window covers out of low-e + thinsulate + fabric. They make a HUGE difference in sub-freezing temperatures, and they’re just plain essential below 5F (-15°C). Here is how we made them:
5- On Second Thought
You can read our second thoughts in each respective installation article listed above. But to sum it up: we would choose exactly the same van insulation strategy if we had to start over! It has served us very well.
Want to know more about winter vanlife? Driving in snow, 4×4, FWD vs RWD, electricity, finding water, finding camp spots, etc.? We wrote a debrief after our first winter full-time in the van (and plan on updating it every winter):
Hi guys!
Because XPS has a maximum temperature of 165, did you notice any melting? Because it could be 80-90 degrees outside, inside of the van could be way hotter and potentially affect the XPS. What did you do to mitigate that?
We didn’t have any issue (FarOutVan #1 was built with XPS as well), and MANY people use that for their floor 🙂
To handle more extreme temperatures, would you suggest a double layer of XPS (attached to the van walls) and Thinsulate or Armaflex as a second layer? Cheers from Italy 😉
I went to the 3M website and it only addressed acoustics. It said nothing about thermal and I believe a Fortune 500 Company would want to sell its product for any purpose it could be utilized and thermal, (heat..etc) was not mentioned at all. I thought I’d share this because the whole debate is confusing for all of us but my novice is steering me towards another insulation type.
I’m currently converting a van for a traveling musician friend based in Texas and really appreciate The time you’ve put into providing all this info-it’s been very helpful with our build. I wanted to pass on some empirical info regarding Lizard Skin. I understand you are primarily cooler weather travelers, with 95F being on the high end of your environment. I’m based just outside Big Bend NP where our summer temps are frequently at or above 115F and this van will spend quite a bit of time in high temp zones. You dismissed Lizard Skin due to the fact that no r-value numbers were available(makes sense for a cold weather application), but Lizard Skin is designed to reduce heat transfer(solar or engine), not insulate, thus no need for r-value ratings. This might be confusing to people not familiar with the terminology or application. It’s also meant to be sprayed inside the van prior to insulation, not outside. I sprayed the interior yesterday and left a sample area(1 section of roof between ribs) unpainted for temperature delta testing. Outside temps were 85F. The un-coated roof section read 96F on an infrared thermometer. The coated roof section immediately adjacent to it read 82F. I also sprayed a sample patch on a piece of corrugated metal painted black(we use these on our cabins). The difference in temps is so profound that I am now considering this product, or an alternative, for our future high sun exposure roof projects. I’m installing the sub-floor in the van today in similar conditions and the interior is cool to the touch. I’m not a professional builder or product rep, so have no skin in the game, but definitely feel this coating deserves consideration of builders that are planning to have a lot of solar exposure, as lower heat transfer means less AC needed. I’m very impressed with the product and wanted to share with your audience. Thank you again for all you do!
How much linear feet did you use ?
Hey!
We made a calculator to find out! This way -> https://faroutride.com/thinsulate/#calc
Hello,
Recently converted a 2023 AWD transit and pretty much followed you insulation method. Our setup utilises the cab space so se turn the seat and use windows cover for insulation. We recently started to use it a < -15 Deg C and notice that there is a big cold air coming in, specially on the driver side and under the driver seat. Is this something you also witness and any thing you did as a work around. At sleep time we do install an additional curtain but when shilling out the curtain is not there to provide a larger living space. Thanks for any advise.
Denis
How did you go about insulating the rear doors?
Didn’t do much in that regard. We simply added some Thinsulate in the cavities (under the plastic panel). We show how to remove the panel here (Step 2): https://faroutride.com/product/transit-rear-door-exit-handle/#installation
Antoine