Take a look at kite Tyvek. It is a lighter, more flexible version of the Tyvek House Wrap with which you are familiar. It is more like fabric than a thin board and it only weighs 1.2-1.3 oz per sq. yard. I use it for my solo tent; I cut a piece about 24" x 80" and put it under the part of my tent floor on which I lie. It weighs just a bit over two ounces and does not have the "static cling" for which House Wrap is well known.

Here is one source:
http://www.kitebuilder.com/inventory/tyvek.htm
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May I walk in beauty.