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Community and Q&A

Insulation suggestion for an Airstream

Thea Tapson | Posted in General Questions on

I have a 1953 Flying Cloud Airstream that will need some serious restoration. I will be completely removing the inner skins and fully expect to find that the insulation in the Airstream is pink stuff riddled with mouse homes (and poop). I’d really like to insulate it well so as to keep the heat out on sunny days, and the cold out on cold nights, as best I can.

Spray foam insulation has been shown to actually harm the soft aluminum skin of the Airstreams, (it can actually bulge) and because it also adheres to the panels, I hesitate to do something that I may one day need to remove by scraping due to faulty electrical or needing to replace a panel from a ding or such. It does offer the best insulation value though, and I’m considering using rigid foam and somehow cutting it to bend around the curved panels.

What I see most often recommended on the Airstreams most popular forum (airforums) is the use of a reflective radiant barrier known as Prodex, which is like the double bubble aluminum foil oh so beloved around here.. (/sarcasm) While they often do install it with an air gap, gluing little foam bits to the inside of the outer skin in order to maintain the air gap required to create an assembly with a higher R value, I remain most definitely unconvinced in using this method as an insulation, and also don’t see as much value in installing a radiant barrier under what should already prove to be a fairly reflective radiant barrier in itself, no? Please tell me they’re not right, there’s hundreds of people restoring these classics and using aluminum foil for their insulation.

If someone has an idea for me on what actually WILL work, I’d definitely appreciate it. The issue with an Airstream, is that I only have a depth of around 1 3/4 inches to work with. I know I won’t have a good chance of high R value no matter what, but what would make the most sense to try to get it a little higher, (and not cost me an arm and a leg like an Aerogel would?) Would using a rigid polyiso and cutting it somehow to bend around the curve be the best option?

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  1. GBA Editor
    Martin Holladay | | #1

    I would probably experiment with layers of thin (1/2-inch) rigid foam insulation, to see if the foam can bend enough to conform to the curves. For sharp curves, maybe you can use multiple layers of fan-fold insulation (a type of thin rigid foam used by vinyl siding installers).

  2. Charlie Sullivan | | #2

    You can get sheets of flexible, elastic foam insulation made for insulating ducts and large pipes, in at least 1" thickness. It even comes in a green "eco" version that is literally dyed green so it must be good.

  3. GBA Editor
    Martin Holladay | | #3

    I'm not familiar with the product, but it looks like just the ticket.

  4. Expert Member
    Michael Maines | | #4

    The R-value of K-flex is only 3.7/in, but the total R-value in such a small space is not as important as it would be in a larger building. It is a vapor barrier (<0.1 perms) which could be good or bad; with good air-sealing it's probably fine, but if warm air gets into the wall assembly, there is a risk of moisture accumulating on the cold interior surface of the aluminum skin, leading to mold and the typical musty RV smell.

    Another option would be lower-density mineral wool boards, such as Roxul ComfortboardIS. It is vapor-open, has higher insulation values, and is flexible enough for your purposes (with some creativity at sharp or 3-D curves). The problem is that it can be hard to get in small quantities.

  5. Joshua Van Tol | | #5

    I think if you found the right installer spray foam might work. You would want to do very small lifts to minimize bulging and perhaps use open cell foam rather than closed cell, which should exert less pressure on the skin, and also be easier to trim after the fact.

  6. Thea Tapson | | #6

    Charlie, the dyed green makes all the difference in the world! ;) Seriously, thanks for the recommendation for the K-flex, I hadn't heard of it, and will be checking it out. I'm sure it's a lot easier to use than trying to figure out the geometry of cutting a curve into rigid foam. Air sealing in an Airstream truly isn't possible, and in hot weather, I'm sure warm air will get into the wall assembly no matter what, so I'll look at the Roxul ComfortboardIS, I'm more familiar with the batt form.

    Joshua, I'm concerned with any future repairs if I use spray foam, because it's a pain to remove, so something that is more readily movable if I ever get a ding in the skin or need to replace some electrical. Martin, I'll look into fan fold insulation, it too is something new to me.

    Thanks guys, any more ideas let me know!

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