What is the preferred material to fabricate piston rings out of? I know of lots of people using viton o rings, but when looking at those the places that sell them say they should not be used on steam or water. There are also lots of people saying cast iron, but then comes the issue of finding a source for it. I kind of like the idea of using plastics. Has anyone ever used ptfe/delrin/nylon? Have you ever heard of someone 3d printing piston rings out of ABS? Another thought was using pvc as it is pretty easy to come by.