3MF vs STL: what is the difference?

What is an STL file?

STL is the oldest and most common 3D print file. It was created in 1987 for the first 3D printers, and it describes the outside of an object as thousands of tiny triangles. Every slicer, and nearly every 3D program, can open one.

That's all it holds, though: the shape. An STL has no colors, no units (slicers assume millimeters), no plate layout and no print settings. A design with several parts or colors comes as several STL files that you line up and set up yourself. The snowman from our Christmas Ornament Set, for example, is five STL files: the whole shape, plus one piece for each of its four colors.

What is a 3MF file?

3MF stands for 3D Manufacturing Format. It was launched in 2015 by the 3MF Consortium, founded by Microsoft, Autodesk, HP and other companies, to replace STL. A 3MF is really a small package, a bit like a ZIP file, that can hold:

• the shape of every part, with real units
• which color or material each part uses
• how the parts are laid out on the build plate, even across several plates
• the print settings, saved by the slicer that made it
• a preview picture

So a 3MF made in Bambu Studio opens with the plate set, the colors assigned and the settings saved. That's the difference between "here's a shape" and "here's a print, ready to go". Bambu Studio, OrcaSlicer, PrusaSlicer and Cura all open 3MF files, though each slicer only keeps its own settings. Our guide to 3MF files covers how to open one and what's inside.

3MF vs STL, side by side

Why is the 3MF smaller when it holds more?

Two reasons. A 3MF is compressed, like a ZIP file. And it stores each corner of the triangle mesh once, where an STL writes the same corner again for every triangle that touches it.

We measured every design in our catalog that comes with both files. In 72 of the 80, the 3MF was smaller, and the typical 3MF was 27% of the size of the STL files for the same design. Most of the few that came out bigger have a sliced copy of the print saved inside the project.

Is 3MF better than STL?

For printing, usually yes. The file type doesn't change how smooth or detailed a print comes out: that's set when the designer exports the shape, and the same shape prints the same from either file. What a 3MF adds is the setup. The colors, the layout and the settings come with it, so there's less to redo and less to guess.

STL still has two things going for it. It opens in anything, including older programs and many design tools. And it's a clean start when you'd rather use your own settings.

Which one should you use?

• You print on a Bambu Lab printer: open the 3MF project in Bambu Studio. Check that the filament colors match what's loaded, then print.
• You use another printer: open the 3MF in your slicer and choose your own printer profile, or start from the STL with the settings you always use.
• You sell your prints: start from the 3MF project when you can. The same saved settings give the same result every time, which matters when you're printing stock.

Our downloads include a 3MF project where it fits, next to the STL, plus a guide with the settings written out. Each model page lists exactly which files you get.

Does Bambu Lab prefer STL or 3MF?

Bambu Studio opens both, but 3MF is its own project format: when you save in Bambu Studio, you're saving a 3MF. A 3MF made for a Bambu printer brings its plates, colors and settings with it, which is why MakerWorld, Bambu Lab's model site, shares its print profiles as 3MF files. An STL works too; you just set it up yourself. New to it? Our Bambu Studio guide walks through a first print.

What about STEP, OBJ and G-code?

These come up next to STL and 3MF, but they do different jobs.

• STEP is a design file, not a print file. Design programs such as Fusion and Onshape save exact curves in it, so it's the file you edit. Bambu Studio and PrusaSlicer can import a STEP and turn it into triangles, but designers usually share STL or 3MF for printing.
• OBJ is a mesh format from 3D graphics and animation. Like an STL, it holds the shape, and it can carry colors and textures in a separate file. Slicers open it, but it brings no print settings.
• G-code is what the printer actually runs: a list of moves, layer by layer, written by the slicer for one printer. You get G-code by slicing a 3MF or STL. A file ending in .gcode.3mf is a 3MF that's already sliced for one printer model.

How to convert 3MF to STL, and back

3MF to STL: open the 3MF in Bambu Studio or OrcaSlicer and choose File, Export, Export all objects as one STL. In PrusaSlicer it's File, Export, Export Plate as STL/OBJ. The colors, layout and settings stay behind, because STL can't hold them.

STL to 3MF: open the STL in your slicer, set it up the way you like (printer, filament, colors, settings), then choose File, Save Project As. It's saved as a 3MF that reopens exactly as you left it.

There's no need for an online converter: it uploads your file to someone else's server to do what a free slicer does in a minute. Our conversion guide has every step, and the fix for files that come out the wrong size.

Converting files for your own printing is fine under our license. Sharing or selling the converted files isn't.

Common questions

Designs from this guide

$3.79 3ML-021 · Ornament set

Christmas Ornament Set

Six flat layered tree ornaments with bold black outlines: a snowflake, a snowman, a candy cane, a gingerbread man, a Christmas tree and a blank name banner you personalize. STL + 3MF · 8.7 MB View model $3.79 3ML-028 · Earring collection

Christmas Earrings

Four pairs of Christmas earrings: gingerbread men, candy canes, snowflakes and Christmas trees. STL + 3MF · 4.0 MB View model $3.79 3ML-014 · Lantern panels

Harvest Lantern Panels

Four light-up Thanksgiving scenes for our Modular Lantern: a pumpkin patch under the harvest moon, a turkey, falling leaves and acorns. STL + 3MF · 3.7 MB View model $2.49 3ML-052 · Worry stone

Worry Stones

Six pocket worry stones with a smooth, deep thumb dip: a classic oval, a rippled oval, a heart, a leaf, a paw and a turtle. STL + 3MF · 8.4 MB View model

Sources: the 3MF Consortium, Prusa Knowledge Base: Export, and our own catalog files, measured October 28, 2026.