You get what you pay for.
1. Ultralight Weight
2. Packability
3. Waterproofness
Pick two of the above, 'cause you can't get all three.
Options 1 & 2 get you Dyneema - because SilPoly will leak after the silicon is abraded; cost goes up.
Options 2 & 3 get you Aqua Quest Defenders because a 20,000 mm water column is good enough; plenty of size options also.
Or
Options 2 & 3 get you 6-mil. Clear Poly Sheeting - 6 Mil, 16' x 100'; you get six DIY tarps 16'x16' with a smidge left over. Not lightweight but will fold small and will be plenty waterproof.
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