RAM Promaster Insulation

Insulation is a highly debated topic in the DIY van conversion world. We’re not really looking to get into that here, our main goal is to show you the process we took and help you along the way for the type of insulation we chose.

After a lot of research, we ended up insulating our RAM Promaster with 1″ polyiso rigid foam. Polyiso has a high R-value and doesn’t absorb moisture, both important qualities when thinking about van insulation. We looked through a LOT of van conversion forums and this method of insulation seemed to have good results.

First order of business was to measure and cut for the larger panels inside the van. I had read about how messy and difficult cutting polyiso could be, but I had no problems using a standard box knife. I kept things running smoothly by making sure I had a fresh blade in the knife. Once the foil wrapping started to bunch, I put in a new blade.

Running the knife along a straight edge a couple times and then folding the panel (effectively breaking the rigid insulation) proved to be the most effective method.  Once folded, I could easily cut the rest of the way through. Boom, done!

After fine tuning the fit of the boards, it was time to adhere the polyiso panel to the inside of our Promaster. I used 3M 90 spray adhesive for its quick cure time and then followed up with a bead of Great Stuff Pro Gaps & Cracks Sealant to make sure it wasn’t going anywhere. I’ve seen others exclusively use Great Stuff Pro, but by using the 3M, I eliminated the need to prop the polyiso up with boards for an extended period of time. Great Stuff foam has a much longer cure time.

You’ll make a lot of progress pretty quickly with the larger side panels. Once you start getting to the smaller and awkwardly shaped ones, your production takes a nose dive. For example, I had to get a little creative to accommodate a crease in the lower side panel.

After cutting out the ceiling pieces, we marked where the ribs of the van would hit the polyiso. This saved us a lot of adhesive spray and time. We used the same technique as before: sprayed adhesive on both surfaces, made a picture frame of Great Stuff Pro on the polyiso board, held the panel in place for a couple minutes, and then foamed around the perimeter.

We continued this process throughout the rest of the Promaster. When it got too tedious cutting out tiny polyiso pieces, we decided to just use the spray foam to fill in the remaining gaps.


We still need to insulate the floor, but in order to do so we first need to remove the factory flooring. Check out Part II here!

Pro Tips:

  1. Keep a fresh blade in your box knife to prevent the foil backing from ripping
  2. Don’t be cheap (I was at first). Buy the Great Stuff Pro Gun and Gun Cleaner!
  3. Start with the easy big panels first to gain experience
  4. Be patient and don’t rush the job. It starts to get tedious once you get to the smaller sections
  5. Be proactive about keeping your Pro Gun clean

Materials/tools used:

  1. Four Polyiso rigid foam boards
  2. Three cans of Great Stuff Pro Gaps & Cracks Sealant
  3. One Great Stuff Pro Gun
  4. One can of Great Stuff Pro Gun Cleaner
  5. Four cans of 3M 90 spray adhesive
  6. Two box knifes and extra blades (I think this style would work better than what I had on hand)
  7. straight edge (I REALLY wished I would have bought one of these. I just used a level I already had)
  8. Tape measure
  9. Three cases of La Criox (I hate this stuff, but I keep drinking it!)

13 thoughts on “RAM Promaster Insulation

Add yours

  1. Thanks for the detailed job report. I found your site from your link on Gary’s DIY Green Camper page. I am about to start converting my promaster. Did you run your wires before insulating or did you just leave what you thought would be the needed pathways? Did you end up insulating the ribs, and if so, with what? I like you multiple adhesive approach for the quick dry time. Anything you would do differently?


    1. Hey TimW, glad you found the information helpful! To answer your questions:
      1. I ran the wires after I did the majority of the insulation. I drew all the electrical out on a piece of paper before starting, which was helpful.
      2. I did insulate the ribs (after running the wiring). I used the Great Stuff foam to fill them in. Word of caution, don’t go crazy with the stuff. This didn’t happen to me, but I’ve read stories of people spraying WAY too much and causing the exterior metal on the van to bulge.
      3. Nothing I would change as of now, I’m pretty happy with how everything turned out!


      1. Thanks, I am going to follow your 2 adhesive approach. It looks in the pictures like you put sound deadening on the wheel wells. Did you also insulate them, and if so, with what?


      2. TimW,

        Nice, let us know how it goes!

        A friend had some extra sound deadening material laying around (what you see in the picture) so I decided to use it, not sure if it made much of a difference though. I built my lower cabinets around the wheel wells, basically boxing them in, and filled the space with standard fiberglass insulation. That made a HUGE difference in lowering the sound inside the van.


      3. Cool. You and I seem to be thinking similarly. I would love to see more pics of your van, including the garage set up. if you are willing to post them or email them to me.


      4. Hey TimW, I’m hoping to get a couple more articles up next month that will show more of the interior. Until then I’d point you towards our Instagram account, it has a few more “real time” images. If you’re still looking for something more let me know and I’ll shoot you a few pics.


  2. I like the video- very informative and great ideas. One question though on this highly debatable topic- is the insulation done with foil side of polyiso against the van or facing towards the inside of the van. Due to the reflective quality of poly and the lighting it can be deceptive to the eye. And either way- how’s that working for you?


    1. Hi AJ,
      I’m glad you found the article helpful! The Polyiso that we used had reflective material on both sides of the foam. So far it’s been working out great! We’ve been in temps as low as 10 and as high as 100 degrees F without any issues.


      1. Thank you for your quick response. The polyiso I have has foil on one side and the other side is white with a clear film as well as logos.


  3. HI there, have you put any paneling up or just the rigid foam for now? I am thinking of insulating now and putting up wood panels next year. have you had any issues with loose foam or squeaks? Great article, cant wait for the next one!


    1. Hi Sam, sorry for the very slow response time. We’ve been busy with other projects. We reinstalled the factory panels after installing the rigid insulation. We originally planned to use wood but the panels had a nice custom fit and finish. Look for more articles coming in the next couple of months.


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