After all this talk here and on other forums about using tyvek or not and its presumed pros and cons, I thought I'd splash out and buy myself 2 sheets of Tyvek 1443R – 1.5 x 3 m and see what the story was.
The idea was to simply glue them together and use it as a tarp. I cut off two test pieces, glued them together with a generic universal glue. As I was pressing down on the two bits the glue was coming through the fabric. I let it dry for half an hour or so, and then for the big test! I had spent hours upon hours constructing an intricate pulley system for the purpose.
….
It tore without putting up any kind of resistance.
The joint held up fine, it was the fabric that came apart. It didn't tear as such, it seperated. Like cotton wool.
And that was it. I might make a bivvy bag out the rest and see how that works out in the rain.

