$10 Tyvek jacket.
The guy basically cuts up a cover all. Not sure how much I agree with the authors waterproof statements. Or what the life expectancy is with this stuff. But it’s being used as tarps and capes over on backpackinglight.com by many users. Now if we could just figure out how to paint this stuff a subdued color… Sounds like acrylic paint or leather dye is the way to go. I think in an emergency this stuff would be very good. It’s VERY lightweight. 8oz a square yard(?) IIRC. If you could add a small strip of Tyvek to cover the nonwaterproof zipper you might have something here.