A very light and somewhat more durable option are polycryo
window covering kits. This stuff is .75mil thickness, and there are other kits for patio doors where the material is 1.5mil thick.
It's fairly durable but once it gets a rip, especially the at the edge, it can 'run' very quickly. However, easily fixed with any kind of tape.
I have a 3' x 6' piece of the .75mil stuff that I've used for a few years as a ground sheet for pack and other gear, draped over and tucked if rain is blowing under the tarp.
Small and weighs 21 grams.
Attachment 189297