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TPU Under-Extrusion After Corners and Retractions

TPU does not like abrupt pressure changes. Under-extrusion after corners is usually caused by filament compression, excessive retraction, too much speed, or drag in the feed path.

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Quick diagnosis

What this guide solves

TPU does not like abrupt pressure changes. Under-extrusion after corners is usually caused by filament compression, excessive retraction, too much speed, or drag in the feed path.

Start with observation first. Do not change multiple slicer settings at the same time or the real cause becomes harder to find.

Best next action

Confirm the symptom

  • Lines go thin right after sharp corners.
  • The first part of a wall after travel looks missing or weak.
  • Extruder clicks or TPU buckles before the hotend.
  • Infill looks fine but perimeters have gaps after direction changes.
  • The issue improves when speed is lowered dramatically.
Root causes

Most likely causes

  • Retraction distance is too high for flexible filament.
  • Print speed or acceleration is too aggressive.
  • Filament path has too much resistance.
  • Pressure advance is too high or not suitable for TPU.
  • Nozzle temperature is too low for the chosen speed.
Fix order

Do this in order

  1. Step 1. Reduce print speed before changing ten other settings.
  2. Step 2. Lower retraction distance and speed; direct-drive printers often need very little.
  3. Step 3. Disable or reduce pressure advance if corners starve.
  4. Step 4. Increase nozzle temperature slightly if extrusion cannot keep up.
  5. Step 5. Make the filament path as short and low-friction as possible.
  6. Step 6. Use fewer rapid travel/retraction events by adjusting combing or avoid-crossing behavior.
Slicer Settings

Settings to check

Use these as practical starting points, then tune against your printer, material, nozzle, layer height, and model geometry. The safest workflow is one controlled change at a time.

Setting AreaWhat to check
Speed20 to 35 mm/s for many TPU profiles.
Retractionstart very low on direct drive; increase carefully only if strings demand it.
Accelerationreduce for perimeters and small features.
Nozzle temperaturetune upward if lines starve after corners.
Infillavoid overly fast sparse infill that shakes flexible filament.
Printer checks

Mechanical and setup checks

  • Direct drive is easier for TPU; Bowden needs slower speed and lower retraction.
  • Check extruder tension so TPU is gripped without crushing.
  • Ensure spool unwinds freely with no tugging.
  • Avoid sharp filament path bends.
Material notes

Filament or resin notes

  • Softer TPU needs slower movement and less retraction.
  • Wet TPU strings and pops; dry it before tuning.
  • Different shore hardness values need different profiles.
Validation

How to prove the fix worked

Print a small rounded-square path test. The correct TPU profile keeps line width steady after corners without turning the whole part into a stringy mess.

After the validation print succeeds, save the exact printer, material, slicer, nozzle, layer height, support, bed adhesion, and cooling setup in Profile Vault so the fix becomes repeatable.

Recommended tools

Helpful tool categories

Only use tools that match the diagnosis. Common helpful categories include PEI cleaning supplies, filament dryers, nozzles, deburring tools, calipers, support-removal tools, and safe resin handling equipment.

Affiliate disclosure: STLBEAST may earn from qualifying purchases when recommended-tool links are used.

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