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3MF files: how to open them, convert to STL, and what they add

Author Redacción TRIDYsign

Published · Updated

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A 3MF file opens in any modern slicer: Cura, PrusaSlicer, OrcaSlicer and Bambu Studio all import it from File, Open, and on Windows the 3D Builder app opens it too, although that one only views and repairs rather than preparing a print. To convert it to STL you do not need an online converter: open it in your slicer, select the object and use Export as STL, accepting that colour, materials, object separation and settings are dropped. Technically, STL stores only a list of triangles and no units, which is why models sometimes import a thousand times too small, while 3MF is a compressed XML container that also stores units, colours, materials, multiple objects and, in slicer project files, the full print configuration. The specification is at version 1.4.0 and since 2025 it is also international standard ISO/IEC 25422.

  • If a 3MF will not open, it is almost always because the program you are using is not a slicer: generic viewers and older mesh editors do not support it.
  • Converting 3MF to STL means opening and exporting in your own slicer; uploading it to a web converter is a detour that throws away the information that makes 3MF worth having.
  • Two different things are called 3MF: a model 3MF, which carries geometry only, and a slicer project 3MF, which also carries the plate, profiles and settings.
  • STL stores no units. That is why a model sometimes imports a thousand times too small: the file never said whether its numbers were millimetres or inches.
  • 3MF is at version 1.4.0, maintained by the 3MF Consortium within the Linux Foundation's Joint Development Foundation, and since 2025 it is also international standard ISO/IEC 25422.
  • A 3MF is internally a compressed container of XML: you can verify this by renaming a copy to .zip and opening it.

Almost nobody searches for "what is 3MF". What people actually need is to open it, convert it to STL, or get it into Cura. So let us start there and leave the theory where it belongs — at the end.

How do I open a 3MF file?

A 3MF opens in a slicer. That is the short path and the one that preserves everything inside the file.

ProgramOpens 3MFNote
UltiMaker CuraYesShips with the 3MFReader and 3MFWriter plugins
PrusaSlicerYesIt is its native project format
OrcaSlicerYesOpens its own and Bambu Studio project files
Bambu StudioYesMakerWorld downloads usually arrive in this format
Windows 3D BuilderYesGood for viewing and repairing; does not prepare a print
Modelling softwareDependsSeveral support it via plugin; do not assume
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    Open the slicer first, then the file

    Do not double-click the 3MF. Open your slicer and use File, Open. That stops the operating system from handing it to a program that can only display it.

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    If asked to open as project or as model, read the question

    Opening as a project also loads the plate, profiles and settings of whoever made it. Opening as a model loads geometry only and keeps your configuration. To print on your own machine, you usually want model.

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    If it will not open, check three things

    That the file is not still inside a half-extracted ZIP; that your slicer is up to date; and, in Cura, that the 3MF plugins are not disabled in the plugin manager.

How do I convert 3MF to STL?

You do not need an online converter. You already have one installed.

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    Open the 3MF in your slicer

    Cura, PrusaSlicer, OrcaSlicer or Bambu Studio. Any of them works.

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    Select the object on the plate

    If the file contains several objects, decide whether you want one or all. Exporting them together fuses them into a single STL and loses the separation.

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    Export as STL

    In Cura it is under File, Export. In PrusaSlicer and OrcaSlicer, File, Export, Export as STL. Choose binary rather than ASCII: much smaller file, nothing lost.

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    Accept the loss

    The resulting STL keeps the mesh and nothing else. Colour, materials, object separation and settings are gone. If someone asked you for the file so they could print it, send the original 3MF.

Can I edit a 3MF?

It depends what you mean by editing.

  • Move, scale, rotate, cut and paint by colour: done in the slicer, no conversion needed. OrcaSlicer and Bambu Studio let you assign colour per face or per object directly on the 3MF.
  • Change the geometry — enlarge a hole, remove a boss, merge two parts: you need modelling or mesh-editing software. Here it may be worth exporting to STL, editing, and rebuilding the project in the slicer.
  • See what is inside: copy the file, rename it to .zip and open it. You will find XML and, in slicer projects, configuration files. It is the fastest way to tell whether you were handed a model or a complete project.

What is the difference between STL and 3MF?

STL dates from the late 1980s and stores exactly one thing: a list of triangles.

STL3MF
What it storesTrianglesMesh, units, colour, materials, multiple objects, metadata
UnitsNot storedStored
Colour and materialsNoYes, via specification extension
Separate objectsNo, everything is fusedYes
Print settingsNoIn each slicer's project files
CompatibilityUniversalVery broad in modern slicers, narrower in old software
File sizeLarger for the same meshSmaller, because it is compressed

Three practical consequences follow, and anyone who has printed for a month knows all three: the part that imports a thousand times too small, the assembly that arrives fused into one blob, and the unanswerable question of what settings the original creator used.

What 3MF is, formally

The 3D Manufacturing Format is maintained by the 3MF Consortium, a Joint Development Foundation project under the Linux Foundation. The specification is at version 1.4.0 and since 2025 it is also an international standard: ISO/IEC 25422:2025. Members commit to royalty-free patent licensing, which is why manufacturers adopted it without a fight.

The core describes the mesh. Everything else lives in extensions, and they are worth knowing because they show where the format is heading:

  • Materials and Properties — colour and multi-material.
  • Production — identifying parts within a package.
  • Slice — pre-sliced 2D data.
  • Beam Lattice — lattice structures defined by nodes and beam diameters.
  • Boolean Operations, Displacement, Volumetric, and Secure Content for encryption.

So can I forget STL?

Not yet. STL is still the language every program understands, which is why it remains the default interchange format on many repositories and print services.

The practical rule: download 3MF when it exists, save your own projects as 3MF, and export STL only when the destination demands it.

Frequently asked questions

Does Cura open 3MF files?
Yes. Cura ships with the plugins that read and write 3MF. If a 3MF will not open, check that those plugins are not disabled, and whether the file is actually another slicer's project.
Which is better, STL or 3MF?
For printing, 3MF: it preserves units, scale, colour, materials and multiple objects in one file. STL remains useful as a universal interchange format because everything reads it.
Why does my model import tiny or enormous?
It is almost always an STL. The format stores no units, so the program has to guess whether the numbers are millimetres or inches. 3MF stores units, so the problem disappears.

Sources

  1. [1]3MF Specification (version 1.4.0 and extensions)3MF Consortium · Standard · accessed July 27, 2026
  2. [2]Cura — 3MFReader plugin in the official repositoryUltiMaker · Manufacturer · accessed July 27, 2026
  3. [3]OrcaSlicer — releasesOrcaSlicer · Manufacturer · accessed July 27, 2026
  4. [4]PrusaSlicer 2.9.6 — release notesPrusa Research · Manufacturer · accessed July 27, 2026
Update history (2)
  1. Added the distinction between model 3MF and project 3MF, and the list of specification extensions.
  2. Initial publication, leading with the operational side (open, convert, edit) before explaining the format.

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