Thermally Insulating a Van

Insulating our van was important for staying cool in the summer, warm in the winter, and, most of all, keeping our water from freezing. We insulated the floors, walls, and ceiling using Polyisocyanurate, foam sealant, and Reflectix. Be prepared to spend most of this project cutting rigid insulation into small squares/rectangles, gluing these to the frame, and spraying foam sealant everywhere else. If you want to save time on this project, skip down to the “Improvements”.

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How To

Before Starting: Drill holes through the floor and install threaded riv-nuts, which will later be used for anchoring the sub floor to the vehicle’s frame. If you are working on this project with someone, work on the insulation and wiring simultaneously, otherwise, be sure to finish the wiring before starting on the insulation. Additionally, cut all of your plywood subfloor before insulating the floor, to avoid damaging the insulation, while dry fitting the cuts. Before insulating the walls and ceiling, install the subfloor to avoid damaging the floor insulation.



Before getting started, be sure that the interior of your car’s cargo area is very clean. Clean surfaces are critical in ensuring proper adhesion of the Polyisocyanurate (Polyiso) to the van using 3M Adhesive. Take some time to sweep the floor and wipe all surfaces with a wet rag. Additionally, make sure that the front seats are protected, by putting trash bags over the back supports and cardboard in the seats.1

The preparation is the same whether you are insulating the floor, walls, or ceiling:

  1. Use a measuring tape to measure the voids that you want to insulate with Polyiso, to determine the dimensions you need to cut the Poliso to. You are only filling voids (relatively flat) with Polyiso, so don’t worry about the tops of ribs on the floor or ceiling and don’t worry about the parts of the wall that aren’t inset. Assign a letter (location on van: floor, walls, ceiling) and number (void within location on the van) to each void,2 writing it both on the van and on a piece of paper, and record the dimensions being measured next to the codes on your piece of paper. For Polyiso thicknesses, we used:
    • 0.5″ for the floor
    • 1.5″ for the ceiling
    • 2.0″ for the walls
    • leftovers for filling odd gaps and small spaces
  2. Using your straight edges, sketch out the dimensions recorded on the Polyiso. The straighter these are, the easier it will be to fit the pieces to the floor.
  3. Using a jigsaw3 (or exacto knife), cut the Polyiso to the dimensions recorded and write the code for that dimension on the PolyisoNote: it is best to cut the Polyiso slightly smaller than the void it needs to fill to ensure a full contact between the two surfaces. When installing the Polyiso, you will match up this code with the void it is referencing. Measuring and cutting all of your rigid foam pieces ahead of time will save you time in the long run.
    • Before cutting, I strongly suggest you put on a respirator, goggles, and skin coverage. Polyiso is very messy and can have negative long-term effects on your health (MSDS).
  4. Read over how to properly adhere the Polyiso and apply foam sealant to the van, then scroll down to the specific instructions for each section of the van: floor, walls, and ceiling.

Adhering Polyiso

The takeaway here is to use denatured alcohol and pay attention to the time between spraying 3M Adhesive and joining the Polyiso to the frame of the van.


  1. Pick out a piece of pre-cut Polyiso and identify where it goes in the van, based on the code.
  2. Wipe both surfaces that are being adhered with denatured alcohol.
  3. Spray both surfaces with 3M Adhesive and wait for the time specified on the can (or longer if it is cold outside4).
  4. Join the two surfaces by lightly pressing them together. You may want to find another object to assist in applying pressure, while you work on adhering other strips of Polyiso.

Foam Sealant Application

You will use foam sealant to fill just what the can says, “Gaps and Cracks”! Foam sealant not only insulates, but also helps lock the Poyiso in place. That said, don’t rely on the foam sealant to hold anything up, that’s what the 3M adhesive is for, but it will certainly help. One of the biggest things to note is that temperature has a huge affect on foam sealant’s expansion time, so, ideally, you will be applying this during warmer months of the year.5,6

In general, foam sealants are very easy to apply, but here are some pointers:

  • Use the right type of foam sealant for the job. “Big Gap Filler” fills all size gaps, but expands further out of small cracks than the “Gaps and Cracks” sealant. This causes less air to get to the sealant in the back of the crack and slows the expansion in this area, preventing air pockets from fully expanding.7
  • Spray the foam sealant at a continuous rate and constant angle, to ensure uniform application. Too little is better than too much, to maximize expansion of the foam. Once the sealant has cured, you can always go back and add more.
  • Spray in such a way that the nozzle tip never touches the foam sealant that is still curing. Doing so will effect the uniformity of its expansion.
  • Spraying on the ceiling takes a little finesse, but, by the time you get here, you’ll have the technique down. If you find that the foam keeps falling off, just do one pass at a time and wait for it to cure. Having the sealant touch a previous pass before it has finished curing can cause it to fall off.
  • Foam sealants are quite sticky and hard to wipe up cleanly, but, if you accidentally drop some somewhere that you don’t want it, wait and let it cure. Once cured, it is really easy to cleanup!
  • In areas where the foam sealant protrudes out past the plane that the paneling will be anchored on, you will have to shave off excess foam sealant. The tricky bit is not accidentally puncturing the vapor barrier on the Polyiso. Using a serrated knife with a long blade (bread knife) works really well for this because you can hold both ends of the knife, so that the center is bowed downward, and slice off the excess. This works best when the foam sealant has fully cured because it will be less messy and make a cleaner cut.
  • Think about where you are applying foam sealant! You don’t want to cover wires or anything that you may want to remove later on. Two particular areas of note are above the rear doors and in the bottom corners to the sides of the rear doors; there are exterior lights that could be a pain to service if they are covered in foam sealant. Additionally, any area you added wires, such as the ceiling lighting, you will want to avoid spraying.


Reminder: Be sure that you have installed rivnuts to anchor the subfloor, cut your subfloor pieces, and checked that they fit before beginning to insulate the floor.


Now that everything is cut, you can start adhering the Polyiso and applying the foam sealant to the floor of the van. I’d suggest starting from front (behind driver and passenger seat) to back and left (behind driver seat) to right (behind passenger seat), to maximize accessibility to each area and decrease the chances of compressing the rigid foam8 by accidentally stepping on it9. Additionally, work in sections, applying the Polyiso and foam sealant, so as to minimize damage.


  1. Apply the half inch Polyiso to the base of the ribs on the floor. Mark where rivnuts are covered.
  2. Add the foam sealant, covering any visible metal between Polyiso strips.
  3. Shave off excess foam sealant with a bread knife.
  4. Continue onto the next section repeating steps one and two until you have finished insulating the floor.
  5. When finished insulating the floor, cut half inch thick wooden blocks and drill a hole in the center. These will go over the rivnuts (in valleys of the floor ribs) to provide support between the van’s metal floor and the subfloor, when compressing this area with the floor anchors.
  6. Lay the wooden block over the Polyiso where a marked rivnut is and trace it. Cut out the Polyiso within the traced box and place the wooden block inside. Repeat this for all marked rivnuts.
  7. Additionally, for rivnuts that are placed on the peak of a rib, you will want to place one washer on top to help minimize compression on the insulation. Repeat step 6, but trace the washers instead of the wooden blocks.


The walls use all types of insulation materials. You will add Reflectix between the walls of the van and the Polyiso to provide an extra vapor barrier.



  1. Cut the Reflectix sheet so that it fits inside the large window voids of the van and install it in the same way you would the Polyiso, using 3M adhesive. The more of the wall you cover, the more protection the metal will have against moisture. You can also add Reflectix in the smaller voids above and below the window voids.
  2. Add two inch Polyiso both on top of the Reflectix and anywhere else in the walls that are relatively flat.
  3. Fill any gaps between Polyiso sheets with foam sealant.



The ceiling has the most curve of any part of the van, so the 1.5 inch Polyiso will have to be cut into smaller rectangles, to ensure sufficient contact. Apply the Polyiso and foam sealant in the same way you did in the rest of the van.

It is hard to get Polyiso inside of the structural supports, so, carefully, fill these with foam sealant. Make sure you haven’t installed threaded rivnuts in the ceiling before this step or the foam sealant will clog the threads.

Note: You may find it hard to get the Polyiso insulation to stick to the ceiling. We were able to get it to stay, but you can also press a piece of plywood against the Polyiso using a stick wedged between the ceiling and the floor.

Finishing Touches

When you’re finished mounting all of your pre-cut Polyiso blocks, you’ll want to use all excess Polyiso and foam sealant to fill additional voids.

Some areas to fill with excess Polyiso and foam sealant include:

  • above the rear doors
  • small crevasses in the walls
  • oddly shaped places that 3M adhesive couldn’t be used to mount the Polyiso


  1. Cut excess Polyiso into small cubes.
  2. Fit as many of the Polyiso cubes into voids around the van.
  3. Fill any additional gaps with foam sealant.

Seat Cardboard? 1

This will prevent your seat from being punctured by any sharp objects during the build.

Why Jigsaw? 3

We started out with an exacto knife and found it hard to cut a straight line, even when using a straight edge. So, we switched over to a jigsaw, which both sped up the cutting and produced very straight lines!

Glue & Cold? 4

We found that the 3M adhesive still works in the cold, but the cure time increases. So, if you find that things aren't sticking, increase the set time before trying to join them.

Foam Sealant Expansion? 5

In colder months, the rate that the foam sealant expands at slows down. So, the air pockets formed will be smaller and, thus, less effective at insulating the van.

Winter Proj? 6

Still find yourself having to do this project in the winter? If so, run some sort of heat source while adhesives are curing and the foam sealant is expanding. In our case, we used a space heater, but some people also use space blankets. The best would be to do this project in a heated garage.

Foam Type? 7

When air pockets can’t fully expand, the R value of the product is being decreased.

Compressing Insulation? 8

Insulation works by having a barrier of air pockets between the area being warmed and the environment. So, when insulation is compressed, it becomes less effective. This is why Polyiso is being installed between the floor ribs and not on top.

Walking on Floor 9

To walk on the floor, after having finished insulating it, and not compress the insulation, lay down a wooden board that spans multiple ribs.




Overall, we were very happy with the end result. The part we weren’t happy about was how labor intensive it was. Some people may also want to consider adding more insulation, if they don’t want to wear as many layers inside their van or worry about their pipes freezing.

When you are just starting out on the van conversion, you will be doing a lot of tasks that are, but don’t feel, productive because they are things you just take for granted in your normal house. So, there is risk of getting burnt out on these steps vs being anal about things such as cabinetry.

Labor: To improve on labor, we would’ve used only foam sealant, leaving out Polyiso all together. Because Polyiso is a rigid foam, its size needs to be exact or smaller than the area it is filling. Measuring and cutting each individual pieces takes a lot of time. Had we only used foam sealant, both of these steps would have been eliminated and we would have saved some money, by buying foam sealant in a larger quantity (Tiger Foam) and getting a bulk discount.

Space: Another thing to consider is how much of your van do you want to: fill with insulation? leave as open space for moving around in? use as storage space? In our case, Philip is very tall, so we opted for adding the minimum amount of insulation by using materials with high R values. It is pointless to buy a van you can stand up in and insulate it so much that you no longer can. Additionally, the space feels more open, which has been especially nice on rainy days, when you don’t want to open the sliding door. The trade off to this is having metal that directly touched the subfloor (the floor gets quite cold in the winter!) or small areas where metal is exposed on the walls.

Floor Insulation Improvements: The subfloor and floor both have an R value of their own, so, technically, there is no direct contact between you and the metal on the floor of the van. But, there is direct contact between the metal and subfloor/floor. If you were to cover the metal ribs in insulation, this would, overtime, lead to the insulation compressing and decrease the R value. To add more insulation the floor, some people add wood supports to increase the thickness of insulation, without it being compressed. In our case, we opted to not do this because it would have decreased the space inside the van. Overall, because hot air rises, the floor is always going to be the coldest area of your van and, with only our body heat and stove providing heat, there is no way for the floor to warm up.

We are considering getting a heat source and are curious how the floor will feel then, but, in the meantime, we are wearing down booties and are quite happy!

In terms of the exposed spots on our walls, there are only two: one behind the bed cushions (so bed cushions are insulating here) and the other by the fridge (so never in direct contact to us, but still letting the cold/heat in).