I almost posted this in the packrafting forum, but y'all might come up with more interesting uses for, or feedback on, the fabric.
Here's the use case in my head: A lightweight waterproof suit that will spend 99%+ of its life in the bottom of a pack; only to be donned upon the rare occassion where icy water, open water, and/or whitewater converge in the context of a mostly overland excursion. In these moments of punctuated dangerosity, a proper drysuit would be preferable, but packing said beast precludes it from happening. So... this mythical drysuit's job would be to keep one's core and limbs dry enough to prevent the underlying layers from loosing their insulative properties long enough to swim to shore and/or reenter the boat (and maintain faculties to paddle to shore). Of course, the main idea is to plan around such incidences, and stay in the boat, but...
In any case, this stuff seems ripe for MYOG experimentation at $5.89 - $14.36 a pop.
There's a thread over on the packrafting.org forums that starts off with the Tyvek question, but introduces some fabric I haven't seen discussed much: Kleenguard by Kimberly-Clark.
The stuff seems to have better breathability (comparison on YouTube) and is more waterproof (another YouTube comparison) than Tyvek. It comes in several different flavors (A10-A90) so here are some stats:
Hydrohead (from brochure):
Cuben - 42.2 cm (.7 oz/yd2 CTF3)
A20 - 72.8cm
A30 - 88.2cm
Tyvek - 112cm
EU Standard for "Waterproof" = 150cm
A40 - 187cm
A60 - 183cm
A80 - 703cm
Gore-Tex - 2,800cm
Gore-Tex XCR - 4,500cm
Gore-Tex ~2,100 gm/m2/24
Gore-Tex XCR ~2,500 gm/m2/24
A60 - 2,800 gm/m2/24
eVent - ~5,500 gm/m2/24
Couldn't find any specifics on weight per yard, but this was mentioned in the packrafting.org post: "The suit weighs only 7 ounces in 2xl." That seems more reasonable than the 4+ lbs. (guesstimating) of a drysuit.
If you go to KC Pro's YouTube channel and search for A30 and A40, there are a few more videos looking at liquid resistance and breathability.
I'm thinking of experimenting with sealing up the seams (even assuming fabric integrity otherwise, the zipper remains problematic) and adding some neck & wrist gaskets...
I'm also ingrigued by the possibility of just buying these things for source material and applying them to other uses. The 4XL suits are still under/around $10.
Ignored in all of the above is the question of durability. I have little expectation that this fabric is some sort of magical solution, but it might maybe possibly kinda work in certain applications. And hey, WPB cuben is currently out of stock anyway.