Extrusion Pressure by Temperature

Extrusion pressure, temperature and filament type

Getting FDM extrusion to behave means juggling three things at once: hotend temperature, volumetric flow and the back-pressure that piles up inside the melt zone. Melt flow scales roughly with Q = w × h × v, while the back-pressure you need climbs non-linearly. Push past the point where the bowden tube or extruder gear can keep up and the filament starts under-extruding, leaving gaps, with the gear grinding away at it.

For a sense of the usual hotend ranges: PLA 190–220 °C, PETG 220–250 °C, ABS 230–260 °C, TPU 220–240 °C, Nylon (PA6/PA12) 240–270 °C, Polycarbonate 260–290 °C. Running hotter thins the melt and drops the pressure, but go too far and you trade that for stringing, oozing and thermal degradation. There's a lag between when the gear turns and when the pressure actually shows up at the nozzle, and to compensate you reach for pressure_advance on Klipper or M900 K<value> linear advance on Marlin. Values land around 0.02–0.05 for PLA, 0.04–0.08 for PETG, 0.06–0.12 for flexible TPU.

Applications

This calculation lets you match hotend capacity to the flow you're after. A stock V6 tops out near 11 mm³/s with PLA, a Revo HF or CHT gets you to 24 mm³/s, and the Bambu X1C high-flow hotend pushes 32 mm³/s. The ELEGOO Neptune 4 Pro and Bambu A1 series arrive with linear advance already dialled in. On a custom Voron, Ratrig or Annex build, run a tower test (pressure advance tower in Klipper, Marlin LIN_ADVANCE_K) any time you switch filament brand or color masterbatch.

FAQ

Why do my corners bulge? The pressure that built up along the straight wall dumps out as the toolhead slows down for the turn. Tune pressure_advance (Klipper) or linear advance (Marlin) until the corners come out crisp and there are no gaps.

Can I just raise the temperature to print faster? Only up to a point. Climb above the recommended range and you start fighting heat creep, stringing and pyrolysis on the heater block. The better move is to add melt area with a Volcano, CHT or Revo HF.

How do I find the highest safe flow? Print a flow-rate calibration tower (OrcaSlicer's Max Volumetric Speed test) at your target temperature and watch for the first hint of under-extrusion or the extruder starting to skip.