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Full Version: Tvyek versus bubble wrap as vapor barrier?
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I was reading Bob's blog post about Richard's van insulation and saw that he had put Tyvek against the metal skin of the van, followed by bubble wrap > Reflectix > 1" styrofoam > NRP board. I'm wondering why one would feel the need to apply a layer of Tyvek beneath the bubble wrap? Wouldn't the bubble wrap itself serve as a vapor barrier? For my insulation I was planning to go with bubble wrap (to serve as vapor barrier and air gap) > Reflectix > 1/2" Polyiso > Coroplast, but if it is worth it to hunt down some Tyvek for the additional layer I will do that. Just trying to plan my layers as carefully as possible to avoid rust/mold issues later on down the road...

I have read up on the subject of insulation extensively and have done my best to search the forums on this so I hope I am not rehashing a question that has already been answered!
Tyvek is NOT a vapor barrier. It says so right on the FAQ page on the Dupont Tyvek site.

Tyvek will do little to nothing against the walls of a van.

You wrap a house in it on the outside of the plywood sheeting, but underneath the siding. It's a breathable material (thus not a vapor barrier) that helps keep water out. A van doesn't need this under it's skin, as it shouldn't have any water under there in the first place.

If it does, then you've got bigger issues to deal with.
That clears it up. Will skip the Tyvek. Thanks y'all
Bigger issues being lack of insulation. Humidity in air condense on wall. Only condensation should be on the window. Do wooden structural walls rot-rust because of water condensation or because of water leaks?
Unless you are leaving an air space, the Reflectix is useless as insulation and you are just wasting your money. According to their website it is R 1 without an air space. For comparison, polyiso is R6. Without an air space it does not work to reflect heat.

I will be putting bubble wrap on either side of the Reflectix to serve as air space, but its always good to have that bit of info in a thread like this in case somebody comes across it in the future! thanks Bob
Right, I see. That makes prefect sense, it holds the space and even adds a little insulation. Good idea!