walmart has 3 diff 1.1ish nylons as i can tell.(vick says there 1.6)
1. some cheap dwr breathable stuff
2. coated with something, almost looks and feels like sil, but it isn't and isn't water proof enough for anything
3. silnylon, i have heard of cases where people have actually found the good stuff at wally world, i myself haven't been so lucky, only 1 & 2.
before when i said to make a 10 x 12 tarp i forgot to mention that once you are more comfortable with tarping you can cut that tarp down to an 8x10 which is a standard 2 person tarp size. that way you won't need top build a diff tarp, just cut some size and weight from the one you already made.
(make the 12ft the 10ft and the 10ft the 8ft so the ridge
line is still running on the long side.)
10x12 should weigh in ball park of 22oz
8x10 about 14oz
i made a 9x10 the other day for a friend and it weighed 15 or 16oz. i can't remember which (owfinc silnylon)
Oh, and yes it is normally cheaper than any online retailer, perhaps close to Noah Lamport but normally chaeper, even dollar bin cheap.