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Insulating Your RV: Thermal Insulation

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This discussion here is not about the solution to the great insulation debate among RV’rs, but my personal view of the many topics involved when insulating an RV. The decisions I take are based on my preferences, my budget, my location(s) and how I’m going to use the van, thus your selection will definitely be different.
I’ll focus primarily on boondocking, where temperatures are mostly unregulated; if you’re spending most of your time on campgrounds, you may opt for more or less insulation materials.

A highly contested subject is the use of vapor barriers in an RV. I regard the outside metal skin of the van as the main vapor barrier, others would like to add a separate layer. The skin of the van will always sweat and some airflow is needed, for this condensation and the existing moisture inside the van, to escape, otherwise it will lead to moisture, mold and rust problems. An extra vapor barrier doesn’t make sense.
At best insulation will keep temperatures regulated for a few hours, but eventually the heat will get in the van and the insulation won’t let it out. Ventilation does the same in hot weather. Winter mornings will be cold, because the same insulation is keeping the warmer outside air out longer. You have to balance its benefits and its drawbacks.
Windows may look like a liability, but in winter they can act like solar heaters, while giving ventilation in summer. In hot climates, some insulation with a good roof exhaust will keep the interior cooler day and night, but at some point it is going to get hot inside even with lots of insulation.

Staying cool starts with a light colored van, that will reflect more of the sun’s rays. And rather more, than less windows to help regulate the inside temperatures during different seasons. Wear more clothes and use more blankets to offset colder winter temperatures.
With a medium roof Ford Transit, where height is critical, I’m inclined to minimize insulation, especially on the ceiling. I’m not willing to lose much interior space to insulation.

Many issues can be defined by identifying the major insulation areas around the RV:

The floor is the least important and matters much less when it comes down to insulation needs. My previous cargo van had a ½ inch layer of foam board with ½ inch plywood on top and I wouldn’t hesitate to do that again. This rigid panel probably works better as noise reduction material than as insulation.


For a well-insulated van we have to protect it against conductive, convective and radiated heat transfer.
Polyiso panels often have a reflective barrier on one side. For that to work properly, we’ll use a 1 inch air gap.
Install horizontal furring strips along the walls with a full inch Polyiso in between, with the reflective barrier facing the skin of the van. The additional 1 inch air space between the foam and the outside skin prevents heat transfer through conduction. The small air gap also limits the possibility of convection and the reflective barrier eliminates most of the radiated heat. You can add another 2 inch layer of blue jeans insulation, to give you even more protection against the elements.
For me, by applying only a single panel of Polyiso directly to the skin of the van, I maximize the interior space, while minimizing the negative properties of insulation (longer cooling off periods at night and colder mornings). At the same time, increased ventilation keeps me cooler during the day and more windows bring in more heat in winter.
In the end your choice will vary greatly, dependent on use, location and your conviction!

The roof gets to withstand the full force of the sun and would benefit most from an increased amount of insulating materials. Polyiso, complemented by an extra layer of blue jeans insulation could increase the R-Value to R-14.
In my van of choice, the medium roof Ford Transit, height is critical; the combined layers of insulation will have to stay within the thickness of the ceiling ribs, to maintain interior standing height.

With reduced insulation, the windows play an important role in heating the interior in winter, while keeping the van cool by means of ventilation. An extra layer of light blocking, heavy double-sided curtains minimizes heat loss/gain in summer, while opening the windows up in winter, will allow for the morning sun to enter and quickly reheat the cool interior.

Roof Vent
The roof vent plays a pivotal role in ventilation, yet at the same time is a major source of heat loss. It is exposed to the sun for most of the day, especially when the van is equipped with solar panels.
Two kinds of insulation will help mediate this.

Cabin Area
The windows in the front cabin could be treated with Reflectix. A better solution is blocking off the driver’s area with an insulated heavy curtain, separating the cabin from the payload area. The curtain would allow continued use of the swiveled passenger chair, while adding more privacy, stealth and insulation. It also reduces winter heating to a smaller interior area.

While not part of the insulation process to keep us comfortable, the fridge needs the same insulation and ventilation to work properly. An extra 2 inch layer of Polyiso can cut the energy use of a 12V Danfoss refrigerator in half and one or more built-in computer fans will improve ventilation greatly.

Insulation Materials

In addition to the items I described above, there are many more materials that can be used to insulate a van. Each has to be evaluated on its properties to decide its suitability for the location and climate where the RV is to be deployed. A good example is fiberglass use in the wet North-West is prone to absorb moisture and will lead quickly to mold and rust. To the contrary, my old Dodge van used it many years without problems, but was stationed in Florida and used mainly in the southern parts of the US.





This material is not intended for use in RV windows. The heat radiated from it will continue to build and could break the glass or ruin window tint or rubber seals.

Polyiso (Polyisocyanurate)

Squeaks while installing, but quiet once in place.


Spray Polyurethane Foam

Blue Jeans Insulation



No matter what kind of insulation you use in your project, the materials have to suit your needs and the climate you’re in. The wide choice of materials offers many opportunities to choose your level of insulation, its properties, like fire resistance or Eco-friendliness and its application methods.

At the top of my list are Polyiso (Polyisocyanurate) (affordable, high R-value, ease of use) and Blue Jeans Insulation (acoustic properties, safe product). At the bottom is Reflectix, often over-hyped and with few useful properties.

Moderately insulate your vehicle, but don’t over-insulate as your van will retain more heat for a longer period on those hot summer evenings and keep your van cooler on cold winter mornings!

I’m not an expert in insulation techniques and these are just my personal views on a complicated issue.

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