STL, OBJ, 3MF or AMF: The Best File Format for 3D Printing
Every slicer accepts several formats, and most people default to STL without thinking. For single-material FDM that is usually fine — but it is worth knowing what each format actually contributes to a print.
The ranking, short version
- 3MF — use it if your slicer supports it (all major ones do). Real units, guaranteed-watertight geometry, colors, and it stores your print settings.
- STL — the safe default. Works everywhere, carries nothing but triangles. Use binary, never ASCII.
- OBJ — only for color/texture printing on machines that accept it; otherwise it adds nothing over STL.
- AMF — avoid for new work. The standard that 3MF superseded; read it, don't write it.
What actually matters for print quality
The format matters less than the mesh inside it. Two things ruin prints: non-watertight meshes (holes, self-intersections) and wrong tessellation density. If your part comes from CAD, export at the right quality rather than decimating later — see tessellation quality explained for what the presets mean.
Coming from CAD?
Convert STEP to 3MF to keep real units, or STEP to STL for maximum compatibility. Either way, inspect the mesh in the 3D viewer before slicing — thirty seconds of rotation catches most faceting and scaling surprises.
Coming from a scan or sculpt?
Scans usually arrive as PLY or OBJ. Convert PLY to STL or OBJ to 3MF, then check the triangle count — sculpts can carry millions of triangles a slicer does not need.