STL vs 3MF: which to use and how to convert
What each format stores, what is lost converting 3MF to STL, and which program opens each one. Written for whoever just downloaded a 3MF and does not know what to do with it.
Updated July 27, 2026
STL or 3MF: what to do with each
Pick what you are trying to do and get the procedure. The full format-by-format comparison sits below.
What to do
Open it with a slicer or CAD, not with a viewer
- A 3MF is not an image or a document: it is a ZIP container holding XML that describes the mesh. It needs a program that understands the format.
- Drag it into your slicer window. Current slicers import 3MF; if yours refuses it, update it before hunting for a converter.
- If it opens but looks empty, it may be a project 3MF: besides the model it stores the plate and the settings of one specific slicer. Open it with the program that produced it, or ask the author for a model 3MF.
- To rule out a damaged file: copy it, rename the copy to .zip and open it. Inside there should be a 3D folder containing 3dmodel.model. If it will not unzip, the download arrived corrupt and has to be repeated.
Rename a copy only. The original file is fine as it is.
Format-by-format comparison
| What it stores | STL | 3MF |
|---|---|---|
| Geometry | Triangle mesh. Every triangle repeats its three vertices, with no shared topology. | Triangle mesh with an indexed vertex list. Same nature, stricter structure. |
| Model precision | Only what the exported mesh has: neither format stores parametric geometry or exact surfaces. | Only what the exported mesh has: neither format stores parametric geometry or exact surfaces. |
| Units | Not declared. The program opening it assumes one, almost always millimetres. | The unit is declared inside the file. |
| Colour and material | Not part of the format. Non-standard extensions exist, with poor cross-program support. | Part of the specification. |
| Per-object settings | No. | Yes: it supports per-object metadata, which is what slicer project files are built on. |
| Multiple objects | Everything arrives as a single block of triangles; the separation between parts is lost. | Each object is stored separately, with its own transform. |
| File size | Text or binary, uncompressed. | Compressed ZIP: for the same mesh, usually smaller. |
| Software support | Practically universal: any program or service in the field accepts it. | Broad across current slicers and CAD. Some older tools and certain services still ask for STL. |
Support changes from one software version to the next, so nothing here claims what any specific program does: check it in the one you use before redoing a file.
Indicative estimate. Real consumption depends on your slicer, your machine and your settings.
How it is calculated
Formula
comparación = matriz de capacidades por formato × soporte por programa. Regla de conversión: 3MF → STL conserva la geometría de malla y descarta color, materiales, unidades declaradas, jerarquía de objetos y ajustes de impresión; STL → 3MF conserva la geometría pero no recupera nada de lo perdido, porque el STL nunca lo tuvo. Corolario: convierte siempre desde el 3MF original, nunca desde un STL derivado.Assumptions
- The 3MF you downloaded may be a plain 3MF or a slicer 'project' (Bambu Studio, OrcaSlicer, PrusaSlicer) with settings inside; they are not the same thing.
- Each program's capabilities are taken from its official documentation, with a date.
- STL stores no units: the same file can be read as millimetres or inches depending on the program.
- Conversion happens on your own computer with software you already run; we do not upload your files anywhere.
Limitations
- It is not an online converter: it explains how to convert with your own software and processes nothing on our server.
- 3MF support varies between versions of the same program; an old version may open the file and silently drop data.
- It does not cover parametric formats (STEP, F3D, SCAD), which are a different conversation.
- A slicer project 3MF may not open correctly in a slicer other than the one that made it.