3MF file vs STL: how to open, convert and share 3MF files

By Ashish · Nov 8, 2026 · ~10 min · 3D printing

A 3MF file is the modern 3D printing format. It can hold the model, its real size, its colors, its separate parts and even your print settings, all in one file. An STL file holds only the shape.

This extra data is why Bambu Studio, PrusaSlicer, OrcaSlicer and MakerWorld now save 3MF by default. It is also why so many people get stuck when a 3MF from one slicer will not open in another. This guide explains what is inside the file, when to use each format, and how to open, convert and fix 3MF files step by step.

Quick answer. Use 3MF for your own projects and multi-color prints, because it keeps units, colors, parts and settings. Use STL to share a simple one-color model with anyone. If a Bambu Studio 3MF will not open in PrusaSlicer or Cura, open it in Bambu Studio and use File, Export, Export Generic 3MF. If that still fails, export STL files.

What is a 3MF file?

3MF stands for 3D Manufacturing Format. It was created by the 3MF Consortium, a group of printer and software makers, as a cleaner replacement for STL. The rules live in the public 3MF Core Specification.

Under the hood, a 3MF file is a ZIP package. ZIP is the same compression format your computer uses for folders you email. Inside the package are plain text XML files. XML is a simple tagged text format, a bit like HTML.

The main model usually sits at 3D/3dmodel.model. It lists every corner point (vertex) and every triangle of the mesh.

The model file also has a unit setting. The specification allows micron, millimeter, centimeter, inch, foot and meter, and the default is millimeter. This small detail fixes one of the oldest STL problems, as you will see below. Slicers can then add their own folders to the package, for example a Metadata folder with print settings, plate layouts and thumbnail pictures.

You can see this for yourself. Copy any 3MF file, rename the copy from .3mf to .zip, and open it like a normal folder. Work on the copy so you never damage the original.

3MF vs STL: what each format can store

STL dates back to the 1980s. It describes a surface as a long list of triangles and nothing else. It has no units, no colors and no idea which triangles belong to which part. A 3MF file stores all of that. Here is the side by side comparison:

File size is easy to estimate for STL. A binary STL uses 50 bytes per triangle plus an 84 byte header. A detailed lithophane with one million triangles is therefore about 50 MB as an STL. The same mesh in a 3MF is usually much smaller, because the ZIP compression squeezes the repeated text.

When to use 3MF and when to use STL

Use 3MF when

• You print in two or more colors with an AMS, a Prusa MMU or a tool changer. The color of each part travels with the file.
• You want to save a project and come back to it later with every setting, support and plate intact.
• The model has several parts that must stay lined up, like a name plate with raised letters.
• You send a print-ready file to a friend who uses the same slicer family as you.

Use STL when

• You share a simple one-color model with the public and do not know which slicer people use.
• You need to edit the mesh in an older or niche program that cannot read 3MF.
• A 3MF keeps failing to load and you just need the shape.

A good habit is to publish both. Printables and MakerWorld both accept STL and 3MF uploads, and many designers offer each one. Our own generators follow the same idea. The Text to STL and 3MF generator gives you an STL for one color and a 3MF that keeps the letters and the base as separate parts, ready for a two-color print. That is the file to grab for 3D printed place cards or personalized Christmas ornaments with names in a second color.

How to open a 3MF file in each slicer

Every major slicer has two ways in. Open Project loads the model and the settings. Import loads only the shape and keeps the settings you already have. Knowing the difference saves a lot of confusion.

When Bambu Studio opens a 3MF that some other program made, it shows the message "The 3mf is not from Bambu Lab, load geometry data only". This is not an error. It means the shape loaded but the other program's settings did not. Pick your printer and filament, slice as normal, and save the project again from Bambu Studio. The warning will not appear next time.

Why a Bambu 3MF will not open in PrusaSlicer or Cura

This is the most common 3MF question right now, and it has a clear technical cause. When you click Save Project, Bambu Studio writes the file using the 3MF Production Extension. That extension lets the main model file stay almost empty and point to each object in its own file under 3D/Objects/. The main model is marked as needing that extension.

PrusaSlicer does not support the Production Extension. It sees the requirement, finds no geometry in the main model, and refuses the file or throws an error. Users have asked for support in the PrusaSlicer issue tracker since late 2024, with comments well into 2026. The request was moved to the discussion board in October 2026, so do not expect a quick fix.

Cura has similar trouble with many Bambu project files. Files you download from MakerWorld are usually Bambu projects, so they hit the same wall.

How to open a Bambu Studio 3MF in PrusaSlicer, step by step

1. Open the file in Bambu Studio or OrcaSlicer. Both are free. You only need one of them for this step.
2. Choose File, Export, Export Generic 3MF. This writes a plain 3MF that follows the core specification, with every object inside the main model.
3. Import the new file in PrusaSlicer. Use File, Import, or press Ctrl+I. In Cura use File, Open File(s). If you are asked, accept a geometry-only load.
4. If it still fails, export STL. In Bambu Studio choose File, Export, Export all objects as STLs. You get one STL per object, which imports anywhere.
5. Set up the print again. Check the size, pick your printer and filament profiles, re-assign colors to each part, and add supports. Then save a new project in the new slicer.

Expect to lose some things on the way. Generic 3MF export keeps the shapes and usually the parts. It does not carry Bambu-specific settings across.

With multi-plate projects, people report that only plate 1 lands where expected while the other parts float at their old positions. Just arrange them again. Painted colors (made with the paint brush tool) often do not survive either, so plan to repaint them.

How to convert 3MF to STL (and STL to 3MF)

3MF to STL: open the 3MF in any slicer, then export. In Bambu Studio and OrcaSlicer use File, Export, then pick one STL for everything or one STL per object. In PrusaSlicer use File, Export, Export Plate as STL. Remember that STL drops colors, names, plates and settings, so keep the original 3MF.

STL to 3MF: import the STL into your slicer and save the project. The 3MF now carries your settings.

Before you save, check the size. An STL designed in inches loads 25.4 times too small, because the slicer reads the numbers as millimeters. Scale it by 2540% to fix it. Once it is saved as 3MF with the right size, the units travel with the file and the problem is gone for good.

Project 3MF vs sliced .gcode.3mf

Bambu Studio can also export a sliced file with File, Export, Export plate sliced file. Its name ends in .gcode.3mf. This is a different thing from a project file. It holds G-code, the line by line machine instructions the printer follows, plus preview images. It is meant to be sent to the printer, not edited.

Other slicers cannot turn that G-code back into a model, and most viewers will report that no 3D model was found. If someone sends you a .gcode.3mf, ask for the project 3MF or an STL instead. It will also only print correctly on the printer and filament it was sliced for.

How to view or share a 3MF file without a slicer

Sometimes you just want to look at a 3MF, or show a print on a website or a shop page. Browsers cannot display 3MF files on their own. The free 3MF to Web converter solves both jobs. Drop in a 3MF from Bambu Studio, OrcaSlicer, PrusaSlicer or Cura and it reads the file inside your browser, so nothing is uploaded. Bambu projects that keep parts in separate files are merged automatically.

The tool lists every part, keeps the stored colors, and plays a layer by layer print simulation at the layer height you choose. You can copy embed code, download one viewer.html file, or download a ZIP. It accepts files up to 150 MB. It is a viewer, not a slicer, so it will not fix a file for PrusaSlicer. It is still a quick way to check that a download really contains the parts you expect before you spend time on it.

3MF troubleshooting: problems, causes and fixes

• PrusaSlicer shows an error or an empty plate. Why: the file uses the Bambu Production Extension. Fix: Export Generic 3MF from Bambu Studio, or export STL files.
• "Load geometry data only" in Bambu Studio. Why: the file came from another program. Fix: accept it, set your profiles, and save the project from Bambu Studio.
• The model is tiny. Why: it is a unitless STL made in inches or centimeters. Fix: scale by 2540% for inches or 1000% for centimeters, then save as 3MF so the units stick.
• Parts float in midair after import. Why: a multi-plate project kept its old positions. Fix: select all, then use Arrange and drop the parts to the bed.
• Colors are gone. Why: it went through STL, or the colors were painted with a slicer-only tool. Fix: re-assign filament per part, or ask for the original 3MF.
• "No 3D model found" in a viewer. Why: it is a sliced .gcode.3mf. Fix: get the project 3MF or STL instead.
• The file will not open anywhere. Why: the download was cut short. Fix: rename a copy to .zip. If it will not open as a ZIP either, download it again.

Next steps

Now that you know which file to pick, put it to work. Make a photo panel with our guide on how to make a lithophane from a photo, then dial it in with the lithophane print settings for Bambu Lab, Prusa and Ender. For a wall light, follow how to make a shadow lamp from any picture. When the print is done, show it off on your own site with the 3MF to Web converter.

Frequently asked questions

What is a 3MF file?

A 3MF file is a 3D printing file. It is a ZIP package that holds the model as XML plus extra data such as units, colors, separate parts, build plates and, in slicer projects, the print settings.

Is 3MF better than STL?

For your own projects, yes. 3MF keeps units, colors, parts and settings, while STL only stores triangles. STL is still the safest choice when you share a single-color model with people who use many different slicers.

How do I open a 3MF file without a slicer?

Drop it into a browser viewer such as the free 3MF to Web tool, which reads the file on your computer. You can also copy the file, rename the copy from .3mf to .zip and open it to see the files inside.

Why can't PrusaSlicer open my Bambu Studio 3MF?

Bambu Studio saves projects with the 3MF Production Extension, which keeps each object in its own file inside the package. PrusaSlicer does not support that extension. Export a generic 3MF or STL files from Bambu Studio instead.

Can I convert a 3MF file to STL?

Yes. Open it in any slicer and export STL. In Bambu Studio use File, Export, Export all objects as STLs. You lose colors, part names, plates and print settings, because STL cannot store them.

Related guides

• Lithophane print settings for Bambu Lab, Prusa and Ender 3
• 3D printed place cards for Thanksgiving dinner
• Personalized Christmas ornaments: 3D print names and photos
• How to make a lithophane from a photo
• Shadow lamp vs lithophane: which to print

Free tools: Lithophane Maker for flat, curved, heart, round and cylinder lamp lithophanes, the Shadow Box Lamp Generator for wall shadow lamps, Text to STL for names and keychains, and 3MF to Web to show your prints on a website. See all tools.