It might HDPE based (smells a bit like wax when burnt) but the flame is blue with yellow tip (which is typical of nylon). It also machines nothing like HDPE (very minimal tearing with nice chips). It might be HDPE with some sort of fibre reinforcement or impregnation or maybe some sort of nylon. I "think" it's used for glide rings/sliding surfaces. Don't think its teflon.