STL vs 3MF Explained

STL has been the standard 3D printing file format since 1987. 3MF is its modern replacement, introduced in 2015 by Microsoft, HP, Autodesk and others. Both work everywhere — but they're not interchangeable, and sending the wrong one can cost you accuracy, colour information or print quality. This guide explains the difference and which file your Australian maker actually wants.

What is an STL?

STL stands for Stereolithography or Standard Tessellation Language depending on who you ask. It describes a 3D part as a mesh of triangles — nothing else. No colour, no units, no materials, no print settings, no multiple parts in one file. Just a watertight collection of triangles in 3D space.

Because STL is so simple, every slicer, CAD program, mesh editor and 3D printer ever made can open it. That universality is why it's still the default export format for almost every CAD tool in 2026.

The downside of being so simple: an STL can't tell the slicer what units it's in. A part designed in millimetres will load identically to one designed in inches — and the slicer assumes millimetres. If your part comes out 25 times too small or too large, the STL was probably in the wrong units.

What is a 3MF?

3MF (3D Manufacturing Format) is a modern XML-based archive that contains the mesh plus everything STL is missing: units (always millimetres), colour-per-triangle, multiple parts in one file, materials, textures, print settings, plate layouts, supports and infill profiles.

When you save a project in Bambu Studio, OrcaSlicer or PrusaSlicer, the .3mf file it produces contains your model and the exact slicer settings you chose. A maker who opens that 3mf sees your intended orientation, supports, infill and material — removing guesswork and producing a more accurate quote.

Which should you send your maker?

If you only have an STL, send it. Every Australian maker can open one and produce a great print. Tell them the intended units, material and any orientation that matters, and they'll handle the rest.

If you have a 3MF exported from your slicer with material, orientation and print settings already set, send that. You'll get a faster quote and the print will match your intent exactly.

If you have CAD source (Fusion 360, SolidWorks, Onshape, FreeCAD), export STEP as well. STEP preserves the original geometry — surfaces, edges, dimensions — so a maker can tweak it without losing precision. STL and 3MF are mesh formats; you can't easily edit them in CAD once exported.

OBJ files are common in art and sculpting workflows (Blender, ZBrush). Most slicers accept them but STL or 3MF is preferred for engineering parts because OBJ doesn't always come through watertight.

STL pitfalls to avoid

Non-manifold mesh: the part has holes, flipped normals or self-intersecting faces. The slicer can't tell inside from outside and produces a confused print. Run your model through Meshmixer, Blender's 3D Print Toolbox or Netfabb to repair before sending.

Excessive triangle count: an STL exported at maximum quality from CAD can easily be 50 MB and 5 million triangles. Most slicers cope but it slows everything down. Export at medium quality unless you need micron-level detail.

Wrong units: see above. Always tell your maker if the part should be in inches or anything other than millimetres.

3MF pitfalls

Slicer-locked settings: a 3MF saved from Bambu Studio carries Bambu-specific profiles. If the maker uses a different slicer they'll have to re-tune. Not a problem in practice (any maker re-checks settings before printing) but don't expect every preset to carry across.

Bigger files: a 3MF with embedded textures and supports can be tens of megabytes. Strip unused plates before sharing.

STEP and IGES

STEP (.step, .stp) and IGES (.iges, .igs) are CAD interchange formats. They preserve parametric geometry — a cylinder is a cylinder, not a 60-sided polygon — so a maker can scale, fillet or modify the part without quality loss. Send STEP whenever you have it; many makers will quote a lower price because they don't need to remesh the part.

Converting between formats

STL ↔ 3MF: any modern slicer. Open the STL, then File → Save Project As 3MF.

STEP → STL/3MF: any CAD program. File → Export → STL/3MF. Choose medium-high quality.

STL → STEP: hard. Mesh-to-solid conversion requires specialised tools (Fusion 360's mesh-to-BRep, Rhino, Spaceclaim). Often easier to redraw the part in CAD using the STL as a template.

OBJ → STL/3MF: Blender, Meshmixer or any slicer.

What about G-code?

G-code (.gcode, .bgcode) is the final machine instructions for a specific printer. Don't send it to a maker — every printer needs its own G-code and the file is useless on any other machine. Always send STL, 3MF or STEP and let the maker slice it for their own printer.

Recommended file to send

Best: STEP + a 3MF reference (gives the maker editable geometry and your intended layout).

Good: 3MF alone.

Fine: STL with a short note describing units, material and which faces are critical.

Avoid: G-code, raw CAD source files (.f3d, .sldprt — the maker probably doesn't have a licence for your CAD program).