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Hello All,
I'm in the planning faze of my vandwelling life and I'm looking into insulation a van. Most likely I'll go with polyiso.

My question:
I've seen some installations with the foil side faced to the inside of the van and others where the foil side is facing the outside. Which is correct?

Thank you
A Future Nomad
The foam insulating board i used has foil on both sides. From Home Depot and Lowes.
Foil can serve two purposes.

1. It can serve as a radiant barrier, to prevent transfer of heat by radiation.  But in order to do that, there must be an air space. So putting it in contact with a vans sheet metal negates that entirely.

2. It can serve as a vapor barrier, to prevent moisture from getting in.  But again, the vans sheet metal is already a perfect vapor barrier, so putting the foil facing the sheet metal again accomplishes nothing.  Putting it facing the inside prevents moisture from infiltrating the insulation from the interior.  But you must tape the seams for maximum effectiveness.  I suspect this aspect of it is more important in bathrooms and kitchens than it would be in vans, unless you're living in the Pacific Northwest.

In short, I'm not really sure foil covered insulation actually does much in a van compared to plain foam insulation.
Backed foam insulation is so much easier to work with.  Get the double sided board.  For the cost difference is not that much.  

Get a long sharp blade, and be carefull.  Take your time.
moisture  infiltrating the insulation  doesn't come into play regarding foam board. I used 1/2 inch, two layers, overlapping seams. easier to fit doing that.  http://www.homedepot.com/p/R-Matte-Rmax-.../100572981
There is always some air gap fitting flat panels to curvy van walls.
(06-25-2017, 08:46 AM)GotSmart Wrote: [ -> ]Get a long sharp blade...

I wish I had invested in a hot knife to cut my foam. Easier, faster. If nothing else, I wouldn't have had styrofoam beads all over the place.
(06-25-2017, 06:41 AM)NJJohn Wrote: [ -> ]Hello All,
I'm in the planning faze of my vandwelling life and I'm looking into insulation a van. Most likely I'll go with polyiso.

My question:
I've seen some installations with the foil side faced to the inside of the van and others where the foil side is facing the outside. Which is correct?

Thank you
A Future Nomad

Foil reflects heat. My theory is if your in a hot climate put foil side out to keep van cool. If you are in a colder climate put foil side in to keep the heat in. So double sided would probably work best.
I used a straight edge and scored the foil/foam with a utility knife. Then just folded the foam away from the cut and snapped it off. Cutting the foil on the other side. If you had Styrofoam beads, that is not the board I am talking about. I am afraid of Styrofoam.
(06-25-2017, 11:09 AM)olddude48 Wrote: [ -> ]Foil reflects heat. My theory is if your in a hot climate put foil side out to keep van cool. If you are in a colder climate put foil side in to keep the heat in. So double sided would probably work best.

I recommend reading post three in this thread.
When I park my maroon van in the sun, I cannot hold my hand on any part of the inner walls, roof except where my foil faced poly insulating boards are against the van walls, roof. It was like an oven when I only had the walls finished. Now with the roof covered, it is a major difference. Look back at my last posts to see the type I used. The foil does make a difference.
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