Polyisocyanurate. Say That Three Times Fast.

I was going to wait and publish this post until I had some cool “in progress” pictures of me actually installing insulation to go alogn with it BUT I’m in this cool “Solo Female Van Dwellers” group on Facebook and someone in there was asking about insulation; sending her a link to this post is going to be easier than copying it all into the small comment box.

There are two main reasons to insulate: sound and weather. When it comes to sound, I’m not as worried about hearing the outside world. In fact, it might be handy sometimes to hear people and animals approaching my van. However, I really love music and it’d be nice to not make it obvious to people in a parking lot next to me that someone is listening to horror movies on Netflix in the back of that creepy unmarked black van.

If you haven’t guessed by other aspects of this blog, I’m a cold-weather person so “just drive south” isn’t always going to be my choice. Others may choose to keep that few inches of space to themselves and not worry about insulating – but I want to toss in at least a little. Note that if I was only planning on doing hot-weather driving I would probably skip most insulation to allow my van to breathe.

To quote someone on another thread, “insulation helps but it’s nothign to lose sleep over unless you don’t have a fan or heater.” Someone else said “The old adage ‘if a little is good, more is better’ is your enemy” when it comes to insualation.

I plan on having both a heater and multiple vent fans, so I’m not worried about having the perfect amount of insulation. I know I want SOME because winter, but if it’s not perfect it’ll be fine as long as we don’t encroach on detrimental territory.

Stolen from Build a Green RV, the important bits are:

  1. “Good thermal insulator (high R value)
  2. “Able to control water vapor to prevent condensation on the van metal – i.e. don’t harm the van.
  3. “Does not absorb water.
  4. “Able to hold up to the relatively high temperatures and vibration over the long term.
  5. “Not squeaky.
  6. “Not toxic.
  7. “Easy to remove.”

Now that I’m covered in Fiberglass…

My van had that horrible pink fiberglass insulation in all the walls and ceilings of the van. It was starting to turn black (whether by dirt or mold, I don’t care to know) and was just plain gross. My parents both urged me to just leave it be and reuse it but I can’t bring myself to do it.

For one, it’s just gross.

For two, fiberglass insulation, when not completely sealed off from your living space, can be a health hazard. It’s an irritant and can seriously bother your respiratory system and your skin. If I want to redo something in my van, I don’t want to have to stress about having that crap around.

For three, it loses it’s R-value (basically, how well it insulates, bigger is better) when it’s compressed. Currently the stuff is about 4″ thick. That means I’m losing 4″ of space all the way around my van. In a house, not a big deal. In a van where I only have 302 cubic feet to live in? Using 60 cubic feet just to insulate? Hell naw. If I can cut down to 1″ of insulation I bring that down to 15 cubic feet.

So What Insulation Should I Use in My Van Conversion?

I’m thinking about ½” of Extruded polystyrene (XPS) for the floor. XPS has an R-value of R-5. I’ll seal the seams with gorilla tape or something similar. It has a high compressive strength hence the floor usage. It’s not environmentally friendly which kinda stinks but I’m going to use it all the same. I can get my entire floor out of 2 sheets if I piece them. This doesn’t include the cab of the van but I’m not really sure my plans for up there yet. If my floor wells aren’t deep (I haven’t seen them yet) I won’t bother filling all of the wells as the air gap might actually be a plus.

Note that XPS is NOT the same as EPS (Expanded Polystyrene) which is basically cheap styrofoam and is awful. Don’t use that stuff. Any moisture will ruin it with time AND it can melt at a low enough point (165F) that vehicle usage against a hot metal body is probably a bad idea.

In the walls and ceiling I’d like to use Polyisocyanurate (Polyiso) (a white foam with foil) because it’s slightly bending and has an R-6 rating. I’ll need ¾-1” of insulation all the way around the walls. The foil on one side doubles as a vapor barrier and a radiant barrier anywhere there’s a slight air gap. Note that it’s nicer on the environment than XPS but XPS does better than Polyiso at temperatures below 50 degrees. Because I’m a snowbird, I might do XPS everywhere instead as they are about the same price at my local Home Depot.

I’ll need some kind of peel-and-stick for the wheel wells like Reflectix or the more cost-effect “any brand of duct wrap” glued down with 3M High Strength 90 and then taped up with foil tape or Gorilla tape. Reflectix has an R-Value per inch of 4.4 and may videos show people using it in the walls as well but that just plain doesn’t make sense. Reflectix requires an air gap to work and I plan on attaching material directly to it for the walls. It would work in the inner cavities of door panels or anywhere where there’s a ¾” gap, but I don’t plan on putting THAT much effort into insulation and I’m leaving the doors as is.

Air Pockets? Oh My!

Something to think about that I didn’t know before my research phase:

The internet tells me that if I create accessible air pockets behind the insulation, I could create moisture traps and thatI must make sure that it’s installed right up against the van body so there are no air pockets and I need to seam all the seams with foil tape and spray foam. I should, in theory, use a spray-foam that has a low expansion rate (like Great Stuff Pro) to attach the insulation. You do need to make sure to only use a thin layer so that it doesn’t distort the van skin. It also takes about 30 minutes to set so I’m either going to need patient friends or some temporary wood struts to hold stuff in place.

I’m not sure yet if I’ll place solid sheets across the van’s ribs or if I will cut it and place it in the gaps. The internet also tells me I should tape up all the edges.

I might do 1” between ribs installed with Great Stuff and then place a solid piece of ½” across all the ribs….If I don’t cover the rins, I do understand that I am creating some definitely thermal bridges where the insulation is missing. However, the excess space is a little more important to me here. A van with thermal bridges is still better than a van with no insulation, right? Decisions, decisions…..

Some people use spray foam inulation everywhere to guarantee no gaps but that’s just terrifying. Can you imagine having to scrap all that out if you ever decide to switch things up? *shivers*

Oh. Quick note for my other newbie friends: I used Great Stuff in a project around my old house. Wear gloves and clothes you can throw away or even a cheap poncho for when doing the ceiling. If you get some on you it will hang out as a weird texture on your skin for a week or two and be completely obnoxious.

What About A Vapor Barrier?

Just no. Just stop. It’s not going to happen.

Look, the van is going to get full of condensation. I can’t help that.

Vapor barriers are only useful if they’re perfect and that’s something I will never claim to be able to achieve. It’s just not worth the effort of trying to put one in. The insulation choices I’ve made above have coatings on them that kind of act like a vapor barrier and that will just have to suffice.

I’d rather just make sure I have enough ventilation to dry the van out and allow the panels to breath instead of trapping in the moisture with an imperfect vapor barrier.

Quote from one of the forums I link to below, “put the insulation in contact with the vans walls to have the dew point occur IN THE rigid insulation between its surfaces where the vapor cannot get (seal the edges and don’t disturb the foil surfaces) that way there is NO vapor where the deep point is so NO CONDENSATE! This is a proven system in modern super insulated buildings (which I have built and it works). This is why a rigid foam that will not absorb water is needed and why foaming the van works and layers of loose fill like fiberglas only won’t.”

Good enough argument for me!

Covering the Windows

In a later step I’ll make some InfraStop or Relectix panels for each window that snap or velcro in place. I need to remember the windshield, too! In the summer I will face the reflective side out and in the winter I will face it in!

Additional Tips

One of the folks in a board stated he ran fishing line through all of his ribs before insulating. This way, should he need to run wiring through them in the future, he has an easy way to run the wires! I think this is brilliant. I’m one of those people who will probably change my van once a week once I move in so having some insight now to help with future flexibility is perfect. I’ll run some thin line (probably not fishing line, but something a little thicker and more durable) down the ribs and tape off the ends to the body of the van.

Many vans have small drain holes to allow water to drip out of the van that has formed on the walls. Don’t block these!

Diesel engines have a LOT of engine noise. The reason I’m not sure what I’m doing in the cab yet is simple: I want extra sound barriers up there! I’m also not sure how I’m going to do the flooring since it’s such a strange shape. The black carpet the van came with up there is doing pretty well, so I’m thinking just to leave the cab as is until I’m ready to add the sound barriers and such.

TL:DR Version


This is my ceiling as it stands today!!
  1. Seal the ceiling with fibreglass resin (okay, I didn’t mention this above, but I’m going to do this to seal all the remnants of the old insulation that I’m having trouble removing
  2. Apply a sheet of 1″ polyiso using 3M 90 Spray Adhesive OR Great Stuff
  3. Seal the edges of the polyiso with Great Stuff Gaps and Cracks PRO using pro gun
  4. Install a badass wooden ceiling


  1. Place just a few wooden boards into the floor wells as future mounting points
  2. Mount 1/2″ XPS to the floor using thin layer of adhesive across the wells
  3. Cover the wheel wells in duct insulation
  4. Place the thinnest plywood I can use on top of the XPS
  5. Install whatever flooring material


  1. Cover walls in 1″ polyiso using 3M 90 Spray Adhesive OR Great Stuff
  2. Seal the edges of the polyiso with Great Stuff Gaps and Cracks PRO using pro gun
  3. Seal cracks between boards with tape
  4. Cover in wood


  1. Nada. No changes. I’m lazy.

As Usual, I Didn’t Pull This Information Out Of My Own Head

So here are the awesome website posts on insulation which I used to make my decisions:

Bonus Tips: How to Google

Do you have a favorite forum site but it has a horrible search function? Did you know you can Google search specifally from just one website?

Example: I love the Promaster Forum but there’s SO MUCH information that searching it can be a pain. Instead, I go to Google and type “insulation site:promasterforum.com”

This will cause all your results to just be from that one website! It’s super useful!!!


(cover image source)

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