Silnylon is great tarp and hammock material. Light and packs down well, especially compared to the blue WW or Harbor Freight tarps.
Cuben Fiber or CF is at this time the lightest tarp material. It also carries one of the highest price points starting right around 300 bucks or so for a finished model. At present time it's also hard to beat vendor price too, due to the initial investment of adhesives and primers needed to get up and running on a single unit.
CF tarps can weight as little as 4-6 ounces, and pack down almost like saran wrap, do not stretch, and are totally waterproof.
CF is also nearly translucent letting way too much light in for some morning sleepers, and for about the same number is considered too loud in a rainstorm. One HF member has purchased and sold two CF tarps for the latter.