the harder the line the better. I like the idea of a glass rod but would you be able to thread it ok?
I made new wing nets for my F31 and used single braid nylon line (like what one would use for dock line) and has worked. Polypropylene line is what is used in some of the "original" I20 tramps as bolt ropes (quotes are because I ain't sure, but the one I rebuilt was likely an original from 1999 and had a polypro rope). something non-compresible is what you want and I think sta-set is probably too compressible.