Fabric Weight and Hydrostatic Head

Cuben isn't really a fabic so not sure as to how they measure hydrostatic head. Cuben as I understand it is a polyester film/spectra fiber laminate. Not a porus woven fabric.

Should handle pressure until a seam failure basically.

If you are using a ground sheet, (or a waterproof pad for
that matter) why should Hydrostatic head make a difference?

>>>If you are using a ground sheet, (or a waterproof pad for
that matter) why should Hydrostatic head make a difference?
<<<

I feel like in spots I've camped this year it's been entirely possible that had heavy rain occured overnight instead of sleeping on saturated ground I would have had running or pooling water.

While the groundsheet in combination with a silnylon bivy has so far worked fine, I want some extra insurace so that if I choose a poor site (either by making a poor decision or due to severely limited site availability) I might be able to at least get up and relocate prior to my sleeping bag getting soaked.

I'm hoping that I can find something with waterproof properties similar to that of traditional tent bottom fabrics, but weighing less. (I've had traditional tents basically set over a puddle and as long as they're seam sealed they won't leak for several hours.)

Maybe I'm just being paranoid but ground conditions and site selection really seems to be tough up here in the Whites for tarp camping. The official spots are often severely overused and form depressions. It's hard to find spots with high ground sloping away on all sides.

When it rains, most people seem to just bail into shelters or use traditional backpacking tents. I want to find something I'm comfortable taking into the worst conditions and not restrict myself to trails with bailout options.