I got some Tyvek from Restore-products.co.uk. It's sold by the meter off the roll and the roll width is 1.4m
The tyvek is type 1422A and is different from the very stiff stuff ( often termed hard surface tyvek ).
1422A is much softer, quieter and is a bit lighter at 41gsm

I'm going to make a ground sheet to go under the flimsy floor of my tent. i plan to make it just that bit smaller than the floor of the tent.

I have discovered that normal PVA wood glue is good for sticking this Tyvek to itself and have used this method to "edge" the groundsheet all the way round. The edge is strong and retains much of the flexibility. The I also tried gorilla glue ( not gorilla wood glue ) but the bond is not as good.

Where 2 edges meet at the corner you have 3 thicknesses of material. I then just used a hole punch to put a hole at each corner and will attach a length of cord for some pegging points.

hope this helps someone. Feel free to add other tips you may know

Interesting. But isn't PVA water soluble?

Charliecres wrote:Interesting. But isn't PVA water soluble?

Once set PVA is water resistant, it will absorb some moisture if immersed for a period of time. Not all white glues are PVA and will not be water resistant when dry.

I've heard varying reports of the waterproofness of Tyvek - Apparently it'll wet out after awhile, but I'm not sure if this depends on the type of tyvek or exposure to contaminants, like with other breathable materials?