...I buy Tyvek by the yard at some art supply stores in the canvas-by-the-yard sections.
(It's used to back the stretched canvas once the canvas it's stretched and stapled on to the frame.)
I'm wondering if home improvement stores would have it--although that might be printed with logo. When a house goes up, you see it stapled onto the outside walls as a moisture barrior before the siding goes up.
I imagine a creative person could use the tyvek mailers from the P.O. that are complimentary (9x12")...!
The question about Dupont..might they have outlet store at manufacturing sights? (Maybe they're not in the U.S.)
Another thought...would printers who print logo on it for whomever, have roll-end left-overs?
The lightest weight fabric I have ever seen is called 'ghost nylon'--it literally whispers against your skin..an outdoor-wear store is using it in a vest right now, with grey trim. I would love to have a light sleeping bag made out of it!
I gather up the cheap yardage at the local superstore (you know, the one that's too huge to hike through..) You won't believe this but I bought the thin Dupont fabric at $1. a yard that the slippery 'stuff sacks' are made of..you know, the orange ones--but my fabric is gray. It was a close-out fabric. I find fabric that are monopolized at a national chain fabric store, too..in the close-out section.
I'm a fabric connosieur, so after I bought ALL 0f that (sorry folks) I bought whole bolts of the very super thin lightweight ripstop nylon until I had 60 or 70 yards. Same price, $1.00/yd. Some was white, some foggy-clear, some pine green, some tan.
This is rain resistant and dries quick and thin enough to make a tent you can fold up into your pocket--well, a safari pocket (6x6x1/2"). That Dupont stuff, though, will even hold and haul water...amazing stuff.
As for sewing, yes you can sew Tyvek. Use slick paint to seal the seams...it's one buck, dries flexible,comes in colors, and can be put in the washer and drier. It was introduced as a T-shirt decorating 3-D paint. You can also use this to spread on tool handles for a better and softer grip.It's in craft stores.
Tyvek, when bent-up enough, eventually will become porous and leak, whereas, nylon and polyester ripstop won't.
Have a look at fabrics used for umbrellas, too, they dry quickly. Pocket-sized 'reflective' blankets made of chome-like 'mylar' (about 4x6') can also be connected into larger sections by using double-stick hem tape* found in your fabric stores.
There are also flexible fabric glues for the nylon things you're making if you don't want to sew, or if you literally want to make something during your adventure on-the-spot.
Luck to you..