Here is why you don’t want to use a thin Teflon tube in your hot end. The pressure will build up and pop a hole in the tube. The PTFE in this hot end was 1.8mm and OD 2.3mm which is only .25 wall thickness. It ran alright for a few hours and then started oozing plastic out every where. This weekend I will modify it to use a ID 2mm and OD 4mm tubing. I’d like to have an inner diameter of 1.8, but I just can’t find it anywhere with a decent wall thickness.