Van Insulation Guide: Make an Educated Decision

Heat Transfer 101

The goal of adding insulation is to combat heat loss. Heat loss happens because of heat transfert (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 van metal surfaces 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 others transfer heat.

Insulating for conduction:

The more dense a material, the closer the atoms are from each others and the more they transfer energy to their adjacent atoms (by physically colliding to each others). Therefore:

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 radiate electromagnetic waves and can heat up other objets at distance (and therefore loose heat themselves). Energy is transferred through the electromagnetic waves, therefore thermal radiation can propage through vacuum (without the presence of matter).

Insulating for radiation:

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:

While heat transfer can be separated in 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 is an insulating material and compare them between each others, 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“; it 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 test ASTM C518 (“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) of migrating towards cold surfaces. The idea is that moist air from respiration, cooking, drying gear, etc. won’t reach cold surfaces and therefore that eliminates 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 take a better informed decision about your insulation:

CONDENSATION AND MOISTURE IN A VAN | WHY IT HAPPENS AND HOW TO CONTROL IT

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 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 and 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 tend to rise and be replaced by cooler air from above. That’s called an air loop and it’s a phenomenon that happen in non-insulated hollow structure, such as in frames and in 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 loose fibers and not itchy
• Good noise insulation
• Can be stuffed in hard-to-reach places

CONS

• More expensive

Bottom word: it’s a popular tried-and-true product that gives a 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 decrease substantially at cold temperature.
• Create air gaps on funky surfaces (which is mostly the case in vans) = water traps.

XPS Rigid Board

Home Depot

• 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

• Create air gaps on funky surfaces (which is mostly the case in vans) = water traps.
• Maximum service temperature: 165F. (dark painted roof will get hotter than that in the sun! source: phys.org)

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 American Scientific Article, 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- Insulation Strategy

Going from theory to real-life implies making compromises; there is no perfect solution! The best van 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 fondation for our floor, it’s quite cheap and 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 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 show on the picture- (noise insulation, but we’d skip that layer if we had to start over)
• 1/2″ thick Plywood
• Vinyl Flooring -not shown on the picture-

4.2- Walls, Ceiling, Overhead cabin & Sliding Door

• THINSULATE

Installing Thinsulate insulation to 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:

1. Cut Thinsulate to size (using tailor scissors)
2. Apply 3M 90 spray adhesive to the van wall and on the white face of the Thinsulate
3. Wait 30-60 seconds for the adhesive to become tacky
4. Press the Thinsulate against the wall
5. That’s all!

How does it performs in real-life? Since we moved full-time in our van (2017), we had anything between -22F (-30C) and +95F (+35C) 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.