How to spot it

  • Bambu StudioInfo: 4 open edges, for two cubes merged with an internal wallTested: Bambu Studio 2.8 on macOS, tested 2026-10-27
  • Bambu StudioError: 4 non-manifold edges, 4 non-manifold verticesBambu Studio source
  • BlenderSelect › Select All by Trait › Non Manifold highlights themBlender manual

Why it happens

  • The same face stored twice
  • Two parts merged without a boolean, leaving an internal wall
  • A stray face sticking out of the surface

In our tests

35/ 78

78 of the 198 public test files had non-manifold edges. After FixSTL’s repair, 35 were free of them.

The two cubes with an internal wall sliced exactly like one clean cube in Bambu Studio, and FixSTL leaves that file unchanged: deleting the wall is a modelling decision.

Public Thingi10K test set, FixSTL engine 0.6.0 (a7ea280), default repair. How we test

How to fix it

What FixSTL does

  • Removes duplicated faces and welds unwelded seams
  • Removes zero-thickness flaps
  • Cuts out a small damaged patch and fills it again, if the patch spans under 15% of the model and the surface moves less than 1%

What it leaves

  • Internal walls left by merging parts
  • Parts that touch along an edge or at one corner

Elsewhere

  • Blender Select › Select All by Trait › Interior Faces, then delete the faces
  • Blender Mesh › Clean Up › Merge by Distance for unwelded seams
Check your STL