PTFE is a very good insulator it also has a huge working temperature range, exceeding all other plastics. I don't know why but if you use PTFE insulation the copper wire is always silver plated. Due to its expense and difficulty in use, this combination is only used in extreme circumstances, UNLESS you want to show off.
I have come across nonscreened twisted pair multicore that has a carbon loaded outer sheath. This is mitigate the effects of dirt from the atmosphere, changing the charecteristics of the cable as it was for external use for cable TV.
Frank