STL vs 3MF: Which File Should You Use?

If you've downloaded 3D models or exported from a slicer, you've probably seen both STL and 3MF files. They're both common formats for 3D printing, but they're built on different ideas and have different strengths. Choosing the wrong one for your workflow is a minor but real source of friction.

STL: the universal geometry baseline

STL (stereolithography) is the oldest and most widely supported 3D printing format. An STL file describes a 3D shape as a mesh of triangles. Nothing more: no color, no material, no layer information, no print settings. Just geometry.

That simplicity is its biggest strength. Nearly every mainstream slicer reads STL. If you send an STL to someone, you can usually be confident they can open it, regardless of what software they're using. It's also easy to inspect. The format is simple enough that many tools can import it without issue.

The tradeoffs are just as clear. STL describes one mesh per file. Color and material assignments aren't stored. Print settings don't travel with the file. If you need color separation between bodies, you'd either export each body as its own STL or step up to 3MF. You're importing geometry and building the rest of your setup in the slicer yourself.

3MF: the full-project format

3MF is an open format developed by the 3MF Consortium (a group including Microsoft, Autodesk, and printer manufacturers) specifically for additive manufacturing. Where STL only carries geometry, 3MF is a container that can hold the model, color and material metadata, multi-body relationships, thumbnails, and more.

PrusaSlicer treats 3MF as its preferred project format. Cura supports 3MF import and export, though project metadata may not round-trip exactly like it does in Cura's own project workflow. OrcaSlicer, being derived from Bambu's fork of PrusaSlicer, reads it as well. Bambu Studio uses 3MF as its native project format and has built its color workflow on top of it.

The important caveat: not all 3MF metadata is portable across all slicers. The geometry will open fine, but color assignments, multi-material setups, and project-specific metadata may not transfer identically from one slicer to another. Each slicer has its own implementation of how it reads and writes the extended 3MF metadata.

The honest split for color printing

Here's the part most converters gloss over: a 3MF can carry color and material assignments, but that doesn't mean every 3MF arrives pre-colored. ButterySpace's 3MF is the bookmark geometry: clean, two-sided, ready to slice. It does not come with colors assigned, and it won't auto-load any.

That's by design. Color is a choice you make with the filaments you actually own, in the slicer you actually use. To print the bookmark in more than one color, you paint or assign the colors yourself, and Bambu Studio's Color Painting brush and per-height color changes both make this quick. The same is true in OrcaSlicer, PrusaSlicer, and Cura: open the file, then use that slicer's color tools. The matched single body STL covers the geometry in mainstream slicers if you just want a clean single-color print.

When to use which

Situation	Reach for
Two-sided or multi-color print in a 3MF-aware slicer	3MF (then paint the colors in the slicer)
Multi-color print in OrcaSlicer, PrusaSlicer, or Cura	3MF (geometry opens; paint or assign colors yourself)
Single-color print in a mainstream slicer	Either works; STL is simpler
Sharing a model file with someone else	STL for maximum compatibility
Saving a full slicer project (settings + geometry)	3MF (if your slicer supports it)
Importing into Bambu Studio with project setup	3MF

What ButterySpace gives you

The bookmark download includes both: a 3MF project file and a matched single body STL for broad slicer compatibility. Same bookmark geometry, two formats, in shared millimetre coordinates. Open the 3MF in a slicer that supports it, or use the STL anywhere. If you use Bambu Studio, the color guide walks through the fastest way to paint the bookmark.