How to spot it

Close-up of one crack in the instrument pod, marked in orange
Close up, one crack is a single line of open edges.
  • Bambu StudioInfo: 4 open edgesTested: Bambu Studio 2.8 on macOS, tested 2026-10-27
  • PrusaSlicerRemaining errors: 4 open edgesPrusaSlicer 2.9.6 source
  • OrcaSlicerCounts open edges as "non-manifold edges"OrcaSlicer source
  • UltiMaker CuraYour model has missing or extraneous surfacesUltiMaker support

Why it happens

  • Seams that look closed but were never welded
  • Faces lost in an export or a format conversion
  • Openings modelled on purpose, such as an open bottom

In our tests

37/ 76

76 of the 198 public test files had open edges. After FixSTL’s repair, 37 were free of them.

In our Bambu Studio test, a block with a missing face and one with its whole bottom deleted sliced exactly like the closed block, so check the layer preview before you repair.

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

How to fix it

What FixSTL does

  • Fills flat and curved holes spanning up to about a third of the model
  • Welds corners that almost touch; nothing moves more than 0.1% of the model’s size

What it leaves

  • Openings larger than that, or where a patch would cross other surface
  • It cannot tell a deliberate opening from a hole; check what was filled

Elsewhere

  • Blender Edit Mode › Mesh › Clean Up › Fill Holes
  • Source model Close the opening and export again
Check your STL