STL, 3MF, OBJ, G-code — what each is for
Four file formats you'll see constantly. Here's exactly when to use which, no jargon.
STL — the lingua franca
.stl stores a mesh — a 3D shape made of triangles. No colours, no print settings, no part hierarchy. Just "this is the surface of this object".
Use STL when: downloading from Thingiverse, sharing with anyone who has a different slicer, or saving a design for archival. It's understood by every 3D-printing tool ever made.
Pitfall: large/curvy models become enormous STL files. A high-detail dragon can be 50 MB. ForgeSlicer's exporter triangulates curves smartly to keep file sizes sensible.
3MF — the modern upgrade
.3mf is what STL should have been. Same triangle mesh inside, but also stores: separate parts (positives + negatives), colours / materials, print orientation, build-plate position, and units (always mm — no guessing).
Use 3MF when: handing off to OrcaSlicer / Bambu Studio / PrusaSlicer. Your part hierarchy survives so the slicer treats positives and negatives correctly. Multi-colour designs need 3MF.
OBJ — the import format
.obj is similar to STL but with optional vertex colours and UV coordinates. It's common in 3D-art tools (Blender, ZBrush) but rare for 3D-printing-first workflows.
Use OBJ when: importing a model from Blender or a sculpting app. ForgeSlicer imports it the same as STL — just the geometry, ignoring textures.
G-code — instructions, not geometry
.gcode is the output of a slicer. It's not a 3D model — it's a list of toolpath instructions for your printer ("move to X120 Y80, extrude 0.4 mm of filament, ..."). One G-code file = one specific printer, one specific filament, one specific orientation.
You never export G-code from CAD directly. The flow is always CAD (STL/3MF) → slicer → G-code → printer.
Designing → save as STL or 3MF (prefer 3MF). Slicing → the slicer makes G-code. Don't share G-code with strangers — it only works for one printer.