That's interesting - I have tried to heat bend UMHW and while it is supposed to soften at a low temperature, I could never get it to permanently bend much. HDPE is closely related to UMHW so I don't know how you accidentally succeeded where I tried & failed . Nylon is also a thermoplastic, so it can potentially heat warp too. There is a special high temperature UMHW called Tivar HOT (its a brand name) that has all the useful polyethelene traits and is very heat resistant.