I suggest that you go and buy some small product actually made from SilNylon, and get a feel for it. It might be good to carry it with you when visiting WalMart, but the feel of real silnylon is so distinctive that you should not really need the sample with you.

Sea To Summit makes some small stuff sacks as well as a tiny folding shopping bag - both out of silnylon. You can use either one of these things, I am sure.

Identification of fabrics by "remote non-feeling" is likely to be impossible.

There are published "burn tests" to help identify the different fabrics, but WalMart frowns on you pulling out a Zippo and burning up little corners of their fabric in the aisle. Some of the fabrics are pretty hard to identify from a burn test, because they may be blends of two fiber types.

Sometimes I can positively tell polyester from nylon with a burn test, but not always.

I also have pretty much given up on finding outdoor fabrics at my WalMarts -- I haven't seen silnylon there in about 2 1/2 years now. Same with coated nylon. found some mosquito netting, though.

Good luck