New Sprinter 144" 4x4 owner. vapor barrier and insulation questions

Found almost exactly what I wanted at a dealer. 144", 4x4, cargo. Has a rear backup camera, driver comfort package (who cares), premium appearance package (which I really don't want, and in my opinion the chrome grill and painted bumper are significantly uglier, though the xenons are nice), and maybe some other crap I couldn't care less about. It doesn't have a few options I would have preferred like the high idle and proximity assist. It was expensive, but I'm pretty much a full timer in the field and my transit connect, while great, is too small and lack of 4x4 is a concern in the rougher stuff. I had to fly to NY to pick it up (I'm based in socal) but I have family here, so it's not too bad.

I'll have a ton of questions. I'll start with the initial stuff. I'll probably go with a slide out bed like the van in the bearfoot theory blog. however, I'll need to insulate to keep the heat out, which was unbearable in my connect. What kind of vapor barrier do you guys recommend? a layer of spray paint? Or is the factory paint good enough? It's probably not super important for socal, but I hope to travel more in between gigs. On top of whatever vapor barrier, I was going to put some 2" rigid insulation (or 2 sheets of 1" for pliability) and spray foam in the ribs and gaps with some reflectix where suitable. That ought to get me to R13-15 in the body. Any thoughts? I'm especially curious about the vapor barrier.

Anyone know of a CAD / 3D model of the sprinter to assist with interior design?



I don't have much experience with van insulation but based on common building science I don't think you need (or want) one.

First of all, you vapour barrier the warm side. In cold climates, vapour barrier goes inside of the insulation. However, you're looking for a vapour barrier to use with insulation that keeps you cool. That would mean the vapour barrier would go right against the metal of the sprinter which should be it's own vapour barrier making the plastic redundant.

That said, vapour sandwiches are a big no-no in home construction. If you consider the metal to be a vapour barrier, I do, adding a second later creates a vapour sandwich. The reality is in a van you'll have a hard time getting a perfectly sealed vapour barrier so you will eventually get moisture in between layers. If that occurs you're better off having no vapour barrier so the moisture can escape.

I personally would skip the vapour barrier in a van build. More trouble than it's worth.


Engineer In Residence
Yep, no vapor barrier needed. You might check out thinsulate, member Hein sells it for a good price. Easy to work with and install, good sound dampening and insulation value. Your van has holes in the lower body panels for the trim. They let lots of water in. Seal them up with some sikaflex before you insulate.


Yep. Already water coming through the holes in the body. What a ****ty design. What's wrong with double sided tape?

Congratulations with the new van! Most all vehicles have some design issues that leave us wondering.

We used 3M Windoweld to seal the shopping cart trim clip holes from the inside. Thinsulate(TM) won't absorb moisture so water will run through and out the drains. Don't drill holes near the bottom of the wall that can let it trickle onto the floor. The bottom of the wall cavity where the drains are is above the floor level. Feel free to call and we can go over it. Our contact info is at
Thanks Hein. I'll be in touch. I'm considering using thinsulate on the doors to keep the weight down on them.

Any more ideas on material to construct the walls with? I'm thinking some light ply with a laminate over it.


Some sort of lost...
Thinsulate is great stuff, Hein is great to work with and very helpful. I’m just finally starting the interior of my sprinter but here’s what I’m doing.

I’m using Raam mat sound deadening on large panels (foil back butyl stuff), 1/2” thick thinsulate (sourced from a clothing place) glued to the exterior walls with 3m 90 adhesive. I’m using this thin layer to basically act as an air gap between the exterior panels and the next layer, which is the low e reflective/radiant insulation from Hein. Then the 2” thick thinsulate. Then reflectix insulation taped over the big openings. Kind of overkill, but I’m attempting to layer a bit, keep some sound deadening on the outer panels and try to reflect heat away as much as I can (my sprinter is dark gray). This is also making sort of a vapor barrier. I also glued a little bit of 1/2” thinsulate over the top just to help absorb vibrations in the plywood. Again, overkill but that’s just what I’m doing.

Wall panels are 5mm birch ply, covered in 1/8” closed cell foam, then marathon fabric.



On my ford van I raam mat butyl sound deadened, 2” thinsulate inside of that, reflectix, then interior paneling. Super quiet, held in heat very well.


Expedition Leader
on the subject of isolation without bulk: nothing touches my mettle (sic). everything is isolated with a bit of #M VHB tape. reduces squeaks, helps hold, makes me happy. YMMV.

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