I've been picking up hints here and there in my ongoing reads of original journals. Can't dredge up all the references at this hour of the day, but Mishach Browning referenced patches in around 1800, saying that during a rain storm he used one of his linen rifle patches "well-greased with tallow" to cover his rifle's lock. In a description of the home life during the same time period on the frontier of western Maryland his wife was carding their own wool and flax to make their own fabric and clothing. It's pretty easy to make the jump that he had at least a little "say" in the thickness of linen he used for patch material.
In another account from about the same year, he mentioned tow. He was carrying it for cleaning his gun, but in this instance snow and hail was getting into his ears as he tried to sleep, so he used some to fashion ear plugs and "slept well as a result."
Gerrard made quick reference to patches a couple of times in his account of a round trip between St. Louis and Taos in 1846-1847, but my memory is foggy at the moment. About all I can dredge up is that it was fabric, and that he didn't specify details.