PTFE tubing: the part that fails silently
The white tube in your hotend degrades with heat and causes under-extrusion that looks like everything else. How to spot it, and why it limits your printing temperature.
PTFE tubing guides filament, and on most non-all-metal hotends a short length of it runs right down to the top of the nozzle. That short piece is a consumable with a limited life, and when it goes it produces symptoms that send people hunting everywhere else.
Two different jobs
- Bowden tube — the long run from a remote extruder to the hotend. Wears mechanically: the bore polishes and widens, especially with abrasive filament, which adds slop to retraction.
- Hotend liner — the short piece inside the heatsink, ending at or near the nozzle. This is the one that matters, and the one that degrades with heat.
Why the liner limits your temperature
PTFE begins to break down above roughly 240 °C. In practice that puts a ceiling on a lined hotend: PLA and PETG are comfortably fine, but sustained printing at 250 °C and above — some PETG profiles, ABS, nylon, polycarbonate — degrades the liner. This is exactly why all-metal hotends exist, and why a machine with a PTFE liner should not be pushed to high-temperature materials however tempting the slicer profile looks.
The symptoms
- Gradual under-extrusion that no amount of nozzle cleaning fixes.
- Clicking from the extruder as it skips.
- Heat creep — jams after long prints, fine on short ones.
- Prints that got quietly worse over months with no single event to blame.
The usual cause is a gap. When the liner shrinks or is not seated tight against the nozzle, molten plastic creeps into the space, cools, and forms a plug. Every subsequent retraction makes it worse.
How to check and replace
Pull the liner and look at the end that met the nozzle. A healthy piece is white, straight, with a clean square end. A spent one is browned, deformed, or has a flared bell shape. Either means replace it.
Two things matter on refitting: cut the end square — a purpose-made PTFE cutter or a very sharp blade against a straight edge — and seat it hard against the nozzle with no gap. The usual method is to loosen the nozzle slightly while hot, push the tube fully home, then tighten the nozzle against it.
Buy the right bore
Standard for 1.75 mm filament is 2 mm inner diameter, 4 mm outer. Tighter 1.9 mm bore tubing exists and reduces slop in Bowden setups, at the cost of more friction. Getting inner and outer diameter right is essential — the fittings depend on the outer diameter.
It costs very little by the metre. Keep a spare length with your spares, alongside a couple of nozzles — the two failures look alike and being able to swap both settles the question in one session.
Check current prices
More guides
-
Belts, tension and layer shifts
Ringing, wavy walls and prints that jump halfway through are usually mechanical. How to tension a belt by feel, and what else causes a shifted layer.
-
Build surfaces compared: PEI, glass and textured plates
Smooth PEI, textured PEI, glass and the rest — what each is actually good at, which filaments they fight with, and when a worn sheet is your real problem.
-
Calibration tools: calipers, gauges and what you actually need
One tool does most of the work and costs about a tenner. What digital calipers are for, and which other measuring kit is worth owning.
-
Finishing tools: deburring, sanding and cleanup
A handful of cheap tools turn a rough print into a finished part. What to buy first, the right sandpaper progression, and why wet sanding beats dry.
-
Hardened vs brass nozzles: when you actually need one
Abrasive filament destroys brass nozzles fast. Which filaments count, what hardened steel costs you in heat transfer, and when brass is still the right choice.
-
Nozzle sizes explained: 0.2, 0.4, 0.6 and 0.8 mm
What changing nozzle size actually does to print time, strength and detail — and why 0.4 mm is the default for good reasons.
Last reviewed 10 September 2026.