Van Conversion Insulation- Don't Overthink it

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Insulation is an important step for your van and definitely takes some prior research and planning. With an open mind,  I have searched to find what simply makes the most sense. Many people make this step way too overwhelming which in return, freaks all of us out! Lets get to it, starting with the basics and then moving into how I chose to insulate my van.

Wait! Before moving onto insulation, you need to make sure your van is ready. This means all of the holes in the van floor are sealed and rust treatment is completed. For rust treatment check out my previous post: Gut Out & Rust Treatment.

Sealing Holes: 

Holes in the floor of your van are inevitable. Once you gut your van out and remove all the original floor, the hardware will leave holes.

You need to seal these holes well in order to prevent any leak issues in the future. This could lead to rust, mold and mildew (which we all know is not what you want).

We reused the same hardware that was there before to seal them back up. You can do this by putting J-B Weld 313119 RTV Silicone Sealant on all of the threads before drilling it in. If you can not find the hardware, you can use this same stuff by itself. 

Apply a big glob onto preferably one finger or two (if you have tiny hands) and cover the hole in a circular motion. The friction will help it stick better. This needs to sit over night without being touched to dry properly. 

Make sure you wear gloves!! This stuff is very strong.

Once you have done this on ALL of the holes, you’re ready to move onto insulation. Make sure you check very thoroughly!

What is insulation and why is it important?

What is insulation?

Insulation is a material that slows the rate of heat transfer. Heat transfer occurs in 3 ways: Conduction, Convection and Radiation.

Conduction occurs when heat moves along a material passing from one molecule to another. This means two different “bodies” pass heat through direct physical contact. See Examples:

  • Touching a pan on the stove and burning your hand
  • Your Van’s wall feeling hot on your hand from radiation (the sun), then conduction transfers heat from the wall to your hand.

Convection occurs in a circular motion when warmer air with faster molecules rises while the cooler air with slower molecules descends. This can occur in your van when using hot devices. The warm air will rise near these devices and cool air will drop near cold surfaces like windows.


  • Hot Air Baloon: The heater at the base of the balloon heats up the air. Of course, this warmer air rises. Then  it gets trapped in the balloon- causing it to rise as well.
  • Air Conditioner: Cold air is released by the AC and since it is cooler and more dense it sinks. The air that is getting warmer rises and is drawn in by the air conditioner.

Radiation Heat transfer through electromagnetic waves.

What controls radiation?

  1. Distance between surfaces
  2. The difference in temperature of the surfaces
  3. The emissivity of the surface

Emissivity= how shiny something is (it’s ability to reflect thermal radiation)


  • Lazers
  • Infrared lamps used to maintain food warmth at restaurants
  • Microwaves
  • The sun

There are a few important qualities to take into consideration when choosing your insulation.

  1. R-Value
  2. Application difficulty
  3. Price

The “R-Value” is a material’s capacity to resist heat transfer. Essentially, this is how good at insulating it is. Now,we have to remember that the R-value is affected by surrounding materials as well. When insulation is placed between high conducting materials like wooden studs, the entire system’s R-Value drops.

For example, using sheep wool on your ceiling or walls between wooden studs can lower the sheep wool’s R-Value. This is because, no matter what you do there will be some gaps between this fluffy material and the wood.

These gaps create convection loops. Convection loops are tiny circular motions of air that cause heat loss.

Framing your floor with wood also drops your system’s R-Value. Every piece of foam board you lay down on your floor is now surrounded by a great heat conductor if you do this.

I chose to not frame my floor because of this reason. I also chose not to because many other great builds I’ve seen (even someone’s 2nd van build)  chose not to. Your van floor isn’t going anywhere. You can use your walls as anchors for cabinets and your bed anyways.  I will be putting wood slats on my walls for anchor points. Framing your floor also take precious height away.

Another point to take into consideration is thermal bridges. These are components in your van that have a much higher heat conductivity than surrounding materials.

Thermal bridges create a great path of least resistance for the dreaded heat to travel. This is most likely the hollow metal framing on your van walls and ceiling. 

I had extra sheep wool bats which I then laid continuously on most of my exposed metal framing to then cover with the walls. I also insulated INSIDE the hollow frame with sheep wool.

This seems excessive but I had extra sheep wool anyways and every bit counts. Your system’s R-value is a combined score from every  aspect of your van. That means thermal bridges, walls, ceiling, floor, windows… everything. If you can cover these thermal bridges then do so. If not, it is not the end of the world. 

Common types of insulation are foam boards, wool and spray foam. These are known as “bulk insulation”.

Bulk insulation traps dry air in lightweight bulky materials. Tiny pockets of air slow down heat transfer by convection. Using insulation with smaller cell sizes prevents the convection within the cell.

Spray Foam

R-Value: 6.5-7
Some sound barrier qualities.
Good for some nooks/crannies. Good for around foam board. Messy and hard to stick to large flat surfaces (might ooze down/fall before drying if its vertical).

Foil-Faced Polyisocyanurate Foam Board

R-Value: 5
Sticks to large/flat surfaces well (walls, ceiling & floor).
Usually has a foil-faced side which creates a radiant barrier as well.
Works well with spray foam.
Not expensive.
Bad for odd/weird areas.

Sheep Wool

R-Value: 3.5-3.8
Has sound barrier qualities
Doesn't support a Flame under 1100F.
Suppresses mold & mildew.
Filters air & improves air quality.
Renewable & sustainable.
More difficult to install on large flat areas.
More expensive.

Extruded polystyrene (XPS) foam

R-Value: 5
Does not support mildew or mold growth.
Long-term & stable R-Value.
High compressive strength.
Unfortunately, it is flammable.


R-Value: 3.2
Thinsulate is a brand of synthetic fiber thermal insulation used in clothing.
Has sound barrier qualities.
Easy to install.
Cheaper to buy locally.
Low R-Value.

You have to figure out if you’re simply looking for the easiest method or if you care about the R-Value.If I was looking for the easiest insulation to install, I would pick thinsulate or sheep wool. It is quick, easy to apply, and you can’t really mess it up. However, sheep wool is also a lot more expensive and it’s R-value isn’t great.

If I wanted a material that just truly inhibits heat transfer better (higher R-Value) I would use some foam insulation and spray foam. However, using just these two is very frustrating  because it takes many many cans to fill in the weird areas with spray foam. Spray foam is also very messy.

So I think a combination is the best way to go.

My insulation experience:

Insulation took me some time and originally I thought I was just going to use Polyiso foam board and Great Stuff Spray Foam.

I quickly realized that this just couldn’t be the cemented decision I have to stick with. I liked the spray foam and foam board a lot.

They also have some of the highest R-Values out there! (this really is  important). If you don’t care about R-Value, why are you insulating in the first place?

I realized Spray foam is great for around every piece of foam board as it is also creates an extra seal around them to help make sure it stays.

Spray foam is also good for really awkward areas. However, sheep wool takes the cake for the odd shapes and spaces…  and it has air filtering qualities. 

So I decided to buy sheep wool. Well, someone offered to buy me something I need for the van and that is what I chose.

All of my worries about how to insulate the super funky areas disappeared. I used the foam boards for the large flat areas and the sheep wool for the really weird ones.

I very pleased with how it turned out and I wouldn’t change anything if I could go back. I also thought I got way too much sheep wool at first.

Then I realized I can use the extra bats of wool I have as a nice insulated layer over most of the thermal bridges (metal framing on walls and ceiling).

What I recommend for insulation

Insulation Application Details:

Applying Polyiso Foam Board:

 You will need to cut the foam board to the sizes of the flat surfaces all along your walls and ceiling. Everywhere there was a “ridge” in the van (even a small one) I would cut it to fit inside of that area. Doing this instead of putting one HUGE piece over the whole panel helps get a great seal behind the board and onto the van wall. This also makes sure no moisture can get caught behind there (to sit and eventually cause rust).

What adhesive do you use with polyiso foam board?

I used 3M 90 adhesive spray. I needed about 6 cans for my van (148 wheel base, 170 inches from the back of the front seats to the back doors).

How to use 3M 90: You need to spray this onto the back of the foam board in the most even layer you can manage. I sprayed it as close to the edges and corners as I could. Then you spray the actual van wall area you are applying it to.

Once sprayed, you need to let it sit for roughly 2 minutes.  When the spray is “tacky” enough, you can apply the board to the wall. You can test for this by gently pressing your knuckle into the sprayed adhesive and pulling it away.

What you want to see is that it sticks to your skin momentarily and then pulls back and leaves nothing behind on your hand. If it does leave some residue on your hand, no biggie! This just means it is not tacky enough and you need to wait a little longer.

Applying Great Stuff Spray Foam:

Great Stuff Spray Foam is pretty fun to use (weird, I know). This stuff has a great R-Value and is also a great adhesive. Once you apply Polyiso Foam Board and it has had some time to dry (30 minutes ish) you can spray this spray foam around all of the edges.

Doing so will ensure no water can seep behind the foam boards and also secures it in place very well. This is how I insulated the major parts of my walls, ceiling & doors.

The picture above shows my ceiling and also how I used sheep wool for all of the funky areas and empty cavities.

That brings me to…

Applying Sheep Wool:

Sheep wool is very easy to apply. All you need to do is rip of the estimated size you think you need and stuff it into whatever area you’re trying to insulate. If you need more you simply rip of more and add it.

This gets a tad bit more complicated when trying to insulate the ceiling with sheep wool. Many people hang string and use it to hold the sheep wool up onto the ceiling until they install their actual ceiling layer.

I recommend Polyiso foam board here. The foam board is much easier to apply to the ceiling, has a higher R-Value and is cheaper.

Applying XPS Foam Board:

Applying XPS Foam Board isn’t too complicated but it’s a tad time consuming. First, You need to buy the right adhesive for this foam. I used Loctite PL-300 Foam Board Adhesive. This is specifically engineered for foam board and will not burn through it like other adhesive materials. 

Once you have cut your foam boards in sections to fit the bottom of your floor, you can lay this adhesive down in vertical lines on all of the raised ridges of your floor. Doing so one section at a time, you lay down the adhesive then carefully lay that section of XPS foam down. Once you lay it down, add weight to it to let it sit for 24 hours to make sure it dries correctly. 

I laid down each section one by one until my entire floor layer of XPS foam was down, then I called it a day to let this foam board sit tightly while weighed down.  

Then I filled around all of the edges of the boards with spray foam. This helps secure them in place and prevents sqeaking from the foam boards rubbing together.

Tip: Use pieces of wood on top to help disperse the weight across the foam to help avoid damaging it:) (Although I stood on it and its perfectly fine!)

Materials Needed:

Materials easier

to find locally:


Polyiso Foam Board 3/4 inc

XPS Foam Board 3/4 inch

Birch Plywood 1/2 inch

Stay tuned for the next post covering the van conversion floor in full detail!

Coming Soon: The Floor!