Voron TPU and Flexible Filament Printing Guide

Materials Printing Guide

TPU (Thermoplastic Polyurethane) is one of the most rewarding materials you can print on a Voron. Finished parts are flexible, durable, shock-absorbent, and chemically resistant. But TPU also presents unique challenges: it is hygroscopic, prone to stringing, and its flexibility means it can buckle in the extruder or bind in the Bowden tube if your setup isn't dialed in. Last updated: May 2025.

This guide covers everything you need to print TPU and other flexible filaments on your Voron: selecting the right shore hardness, configuring your direct drive extruder, tuning retraction and speed settings, drying filament, and Voron-specific tips for the Clockwork, Clockwork 2, Galileo, and Orbiter extruders. Whether you're printing 95A durometer TPU for functional parts or 60A-80A for gaskets and vibration dampeners, these settings will get you reliable results.

Shore Hardness Selection

TPU is measured on the Shore hardness scale, typically Shore A for flexible filaments. Lower numbers mean softer material:

Recommendation for Voron: Start with 95A TPU (e.g., NinjaTek Cheetah, SainSmart TPU) if you're new to flexible filaments. 85A-92A (e.g., NinjaFlex, Polymaker PolyFlex) works well once you have retraction tuned. Below 80A, you need a geared extruder with a very short filament path and the extruder tension carefully adjusted.

Direct Drive Setup Requirements

Voron printers use direct drive extruders, which is essential for TPU. Bowden setups are nearly impossible with flexible filaments because the filament buckles inside the tube. Here is what you need for each Voron extruder:

• Clockwork 1 (Afterburner): Works with 95A TPU at moderate speeds. The filament path is short but has a slight bend. Ensure the idler tension is not too tight — overtightening can cause the filament to deform and jam. Use the standard 2.5mm drive gear engagement.
• Clockwork 2 (StealthBurner): Excellent TPU performance. The gear ratio (7.5:1) provides plenty of torque, and the short straight filament path minimizes buckling. Available in gear and belt-driven versions — both work well. Use the CW2 TPU mod (printed filament guide insert) for best results with softer materials.
• Galileo/Galileo 2: The planetary gear system provides high torque, making it excellent for TPU down to 70A. The filament path is straight and short. Reduce tension to the minimum that still drives the filament without slipping.
• Orbiter V1.5/V2.0: Compact geared extruder. Works well with 85A+ TPU. The gear engagement is fixed, so you rely on the tension arm adjustment. Back the tension screw out 1-2 turns from the ABS setting.
• Sherpa Mini: Good for 85A+ TPU. The geared design provides sufficient torque. Use the shortest possible PTFE tube between extruder and hotend.

Key modification: For soft TPU (below 85A), print a filament guide insert that creates a completely straight path from the extruder gears to the hotend heat break. Many Voron community mods exist on GitHub for this purpose.

Retraction Tuning for TPU

TPU behaves differently from rigid filaments during retraction. Too much retraction distance or speed will grind the filament, causing jams. Too little retraction results in stringing and oozing.

• Retraction distance: 0.5-1.5mm for direct drive (start at 0.8mm). This is significantly less than the 2-5mm used for PLA or ABS. Excessive retraction pulls the flexible filament back past the gears, causing deformation.
• Retraction speed: 10-25mm/s (start at 15mm/s). Faster speeds can cause the filament to strip at the hobbed gear. Slower speeds may not clear the nozzle quickly enough for clean travel moves.
• Deretraction (unretract) speed: 10-20mm/s. Slower deretraction reduces the chance of the filament bunching up and jamming.
• Wipe while retracting: Enable this in your slicer. A small wipe movement (0.5-1mm) before retracting helps clean the nozzle tip.
• Extra restart distance: 0-0.2mm. Some TPUs expand slightly after compression, so you may need minimal extra restart to avoid blobs on seam points.

Run a retraction tower from 0.5mm to 2.0mm in 0.25mm increments to find your optimal value. Print two small towers placed 50mm apart — the stringing between them is your diagnostic target.

TPU 95A Starting Profile (OrcaSlicer / SuperSlicer):
  - Retraction length: 0.8mm
  - Retraction speed: 15mm/s
  - Deretraction speed: 15mm/s
  - Retract on layer change: yes
  - Wipe distance: 0.5mm
  - Extra restart: 0.0mm
  - Z-hop: 0.2mm (disabled for TPU if possible)

Speed and Flow Settings

TPU requires slower speeds than rigid filaments because the material compresses under the extruder gear pressure, leading to inconsistent extrusion if you print too fast.

Flow calibration: Always run a flow calibration for each new roll of TPU. Use the standard 20mm x 20mm single-wall cube and measure wall thickness. Adjust flow ratio until walls measure exactly your nozzle width. TPU flow can vary by 5-10% between brands and even between spools of the same brand.

Filament Drying Requirements

TPU is extremely hygroscopic — it absorbs moisture from the air rapidly. Wet TPU produces bubbles, popping sounds, stringing, and poor surface quality. The surface can look cloudy or matte when wet.

• Drying temperature: 50-60°C (do not exceed 65°C or the spool may warp). Dry for 6-8 hours in a filament dryer or food dehydrator.
• Dry box printing: TPU prints best directly from a dry box. After drying, transfer the spool to an airtight container with desiccant (silica gel) and feed the filament through a PTFE tube directly into the extruder.
• Humidity indicator: If you hear popping or see steam at the nozzle, stop and dry the filament immediately. The moisture degrades the polymer and can cause permanent damage with prolonged printing.
• Storage: Store TPU in a sealed bag with desiccant at 20-30% relative humidity. Even overnight exposure to ambient air can require re-drying.

Voron-Specific Tips

• Chamber temperature: TPU does not require a heated chamber. The enclosure can remain open or closed. However, if the chamber is above 40°C, TPU may become soft before reaching the nozzle, causing jams. For TPU, keep the chamber below 35°C — open the enclosure doors or remove the top hat panels.
• Nevermore filter: TPU produces less fume than ABS, but some brands emit volatile compounds. The Nevermore carbon filter helps keep the air clean even at low chamber temperatures.
• Build surface: TPU adheres well to PEI sheets (smooth or textured) at 40-60°C bed temperature. Use a glue stick or Magigoo on smooth PEI for very soft TPU to prevent over-adhesion. TPU can bond permanently to bare PEI if the bed is too hot or the material is very soft.
• Z-offset: A slightly higher first layer (0.28-0.32mm on a 0.2mm layer height) helps avoid nozzle dragging in soft TPU. Too much squish causes the first layer to ripple.
• Part cooling: Use minimal or no part cooling for TPU. 0-20% fan speed is typical. More cooling causes layer separation and brittleness in flexible materials.
• Klipper pressure advance: Start with 0.03-0.06 for TPU (lower than ABS/PLA). Run the pressure advance tuning tower to find your exact value. About 20% lower pressure advance than PLA is a good starting estimate.

Troubleshooting Common TPU Problems

Recommended TPU Filaments for Voron

• Polymaker PolyFlex (95A): Excellent dimensional accuracy, good layer adhesion, consistent diameter. The gold standard for Voron TPU.
• NinjaTek Cheetah (95A): Slightly softer feel than PolyFlex, great for functional parts. Works well in Clockwork 2 and Galileo extruders.
• NinjaFlex (85A): Very good flexibility, prints well in geared extruders. Requires careful retraction tuning.
• SainSmart TPU (95A): Budget-friendly option with decent quality. Good for large prototype parts where cost matters.
• Overture TPU (95A): Affordable and reliable. Slightly more stringy than PolyFlex but consistent diameter.
• Recreus FilaFlex (82A-95A range): Spanish brand with wide hardness range. Their 82A variant is excellent for vibration dampening parts.