Polycro is the thin film they put on window glass. It's very puncture resistant, has high shear strength, and is very light and compressible. On the down side, dirt clings to it like a magnet - which why it clings to glass. I rank it highly for a ground cloth material. I pack mine in a sandwich bag.
The silnylon flooring on Tarptents is pretty darn durable. I wouldn't worry too much about needing the extra protection on High Sierra granite.
