Pressure Advance / Linear Advance Tuning

The Physics of Filament Pressure

Inside a heated hotend, filament behaves somewhat like a compressed spring. As the extruder pushes molten plastic into the nozzle, pressure builds inside the hotend and forces material out through the nozzle opening. The problem is that this pressure does not disappear instantly when the printer slows down or changes direction.

When the printer reaches a corner or begins decelerating, residual pressure inside the nozzle continues pushing filament out for a brief moment. This creates common print artefacts such as blobs on corners, rounded edges, uneven line widths, and inconsistent extrusion through speed changes. These pressure fluctuations become even more noticeable at higher print speeds.

Pressure Advance in Klipper and Linear Advance in Marlin are designed specifically to solve this problem.

Rather than reacting after pressure builds up, the firmware predicts these changes in advance. To relieve pressure early, extrusion is slightly reduced before the printer slows down. The printer accelerates again, and extrusion is briefly increased to rebuild pressure ahead of time. The result is cleaner corners, more consistent extrusion, sharper details, and smoother transitions between fast and slow movements.

Finding Your K-Value

Pressure Advance uses a tuning value commonly referred to as the K value. This number controls how aggressively the firmware compensates for pressure changes inside the hotend.

Different printer setups and materials require different K-values. Direct drive printers generally use much lower values, while Bowden setups often require significantly higher compensation due to the longer and more flexible filament path.

For many direct drive printers, PLA commonly falls somewhere around 0.02 to 0.1, while PETG may require slightly higher values. Bowden systems can often range much higher depending on tube length and material behaviour.

The best way to tune pressure advance is by printing a dedicated calibration pattern while testing different K values. The goal is to find the point where corners appear sharp and consistent without introducing gaps or inconsistent extrusion at line starts.

In Klipper, the value is adjusted using the SET_PRESSURE_ADVANCE command before printing the calibration pattern. Once the best value is found, it can then be saved permanently in the printer configuration file. Marlin uses a similar system called Linear Advance with slightly different commands, but the tuning process follows the same principle.

Per Filament Calibration

One of the most overlooked parts of pressure advance tuning is that different materials behave very differently under pressure.

PLA, PETG, ABS, and TPU all flow differently due to their viscosity, elasticity, and printing temperatures. A K value that works perfectly for PLA will rarely produce ideal results with PETG or flexible materials.

For the best print quality, pressure advance should be calibrated individually for each material type you use regularly. Many users either label calibrated values directly on filament spools or save them inside dedicated slicer profiles for effortless switching between materials.

Fortunately, the calibration process itself is relatively quick, and the improvement in corner quality and extrusion consistency is often immediately noticeable.

Combined with Temperature Tuning

Pressure Advance works best when paired with proper temperature calibration.

Print temperature directly affects how easily molten filament flows through the nozzle. Higher temperatures reduce viscosity, meaning the filament flows more freely and creates less pressure buildup inside the hotend. Lower temperatures increase resistance and often require slightly more compensation.

Because of these factors, changing print temperature can alter the ideal pressure advance value for a filament. This is why temperature tuning should always be completed before calibrating pressure advance.

A optimal workflow is to first run a temperature tower to lock in the best print temperature for the filament and then complete pressure advance tuning afterwards. Together, these two calibrations can produce some of the most noticeable print quality improvements possible on an FDM printer.