STL vs 3MF: which file format for 3D printing

STL is the universal 3D-printing format — a plain triangle mesh of your model's surface that every slicer and printer accepts. 3MF is a newer format that stores the same geometry plus extras: real-world units, color and materials, multiple parts, and even print settings, all in one compact file. For a simple single-color print either works; reach for 3MF when you want units and settings baked in, and STL when you need maximum compatibility.

The quick answer

• STL — geometry only, works absolutely everywhere. The safe default.
• 3MF — geometry plus units, color, multiple objects and print settings, in a smaller, more robust file. Great with modern slicers.

What is an STL file?

STL has been around since 1987 and describes a model as an unstructured mesh of triangles — just the surface, nothing else. It carries no color, no materials, and crucially no units, which is why a model sometimes imports at the wrong scale and has to be resized. STL files also tend to be larger and can pick up mesh errors like flipped normals or gaps. Its huge advantage is universality: every slicer, printer, and tool reads STL, so it's the format that always just works.

What is a 3MF file?

3MF (from 2015) is a modern format built as a small compressed archive of XML. It stores the geometry and a lot more: explicit units so scale is never ambiguous, color and materials, multiple objects and their arrangement, metadata, and even slicing/print settings. Files are typically smaller than the equivalent STL, and the format has built-in validation that avoids many common mesh problems. Modern slicers — PrusaSlicer, Bambu Studio, Cura — support 3MF and increasingly treat it as their native project format.

When to use which

• Use STL when you want maximum compatibility, you're printing a simple single-color part, or a tool or service only accepts STL.
• Use 3MF when you want units carried with the file (no scaling surprises), you're doing multi-color or multi-part prints, or you want to preserve print settings and hand off a ready-to-slice project.

For most makers printing one part in one color, the practical difference is small — pick STL for safety or 3MF for convenience. As slicers keep moving toward 3MF, it's a good habit to reach for.

What 3DGEN exports

Every 3DGEN generator lets you export both STL and 3MF, so you're never locked in. If you're on Bambu Studio, 3MF is the smoother choice; if you want the most universally accepted file, grab the STL. Either way the model is built right in your browser and never leaves your device. Guides like making a lithophane from a photo use exactly these export options.

FAQ

Which should I pick by default?

If your slicer is modern (PrusaSlicer, Bambu Studio, Cura), 3MF is a great default because it keeps units and settings with the file. If you're unsure what will open it, STL is the universally safe choice.

Does STL lose the scale of my model?

STL has no unit information, so a model can import at the wrong size and need rescaling. 3MF stores units explicitly, which avoids that ambiguity.

Do all slicers read 3MF?

The major modern slicers do. Some older or niche tools still expect STL, which is why it remains the safe fallback.