STL files have been synonymous with 3D printing since the format was developed by 3D Systems in 1987. Their ubiquity is a historical artifact as much as a technical endorsement: STL was the only widely supported format for FDM's first decade and a half, so every slicer, every printer firmware, and every model repository grew around it. The format works — but it was designed for a world of monochrome resin stereolithography at industrial scale, and it carries those constraints into every modern desktop use case.
What STL Gets Wrong
An STL file contains exactly one thing: a triangle mesh representing a closed solid surface. It stores vertex coordinates and surface normals for each triangle and nothing else. There are no material properties, no color information, no unit specification (coordinates are dimensionless — the slicer infers units), no support for multiple bodies in a single file, and no metadata of any kind. The ASCII and binary variants add nothing of substance.
The practical consequences accumulate in real workflows: multi-part assemblies require multiple STL files and manual assembly in the slicer; multi-color designs require separate per-color STL files and tedious alignment; material assignments must be communicated out-of-band (a text file, a filename convention, a README); and the lack of orientation data means slicers must infer or ask about preferred print orientation. None of these are technical problems — they're design limitations that engineers in 1987 didn't need to solve for their use case.
What 3MF Provides Instead
3MF (3D Manufacturing Format) is an open standard maintained by the 3MF Consortium, with members including Microsoft, Autodesk, Stratasys, Ultimaker, PTC, and others. The file format is a ZIP archive containing XML files for geometry, materials, thumbnails, relationships, and custom extension namespaces. This container structure allows the format to evolve by adding extension specifications without breaking backward compatibility.
The base specification includes explicit unit declarations (millimeters, inches), transform metadata for object positioning and orientation, support for multiple objects in a single file, and a defined color model for per-face and per-object color assignment. Extension specifications add multi-material support, beam lattice geometry, volumetric data, and production workflow metadata. A 3MF file for a multi-color Bambu print contains color assignments, object placements, print settings, and a thumbnail image — everything the slicer needs to reconstruct the print without any out-of-band information.
Slicer Support
Bambu Studio, OrcaSlicer, PrusaSlicer, and Cura all support 3MF import and export. PrusaSlicer and OrcaSlicer use 3MF as their native project format — the .3mf project file saves not just geometry but full print settings, support structures, and modifier meshes. Loading a .3mf project file restores the complete state of a print job without reconfiguring settings from scratch. This is functionally a massive improvement over STL for any print that required more than default settings.
Bambu Studio's multi-color 3MF export contains color painting data that can be re-imported to restore a painted multi-color setup — a workflow impossible with STL. For users running multi-color printers (Bambu AMS, Prusa MMU), 3MF is not just preferable but necessary for lossless project transfer.
Repository Adoption
Thingiverse, Printables, and Makerworld all now accept and serve 3MF files alongside STL. Printables (Prusa's platform) actively encourages 3MF uploads and renders embedded thumbnails from 3MF files in listings — a user experience improvement over STL listings that require separate rendered previews. Makerworld (Bambu's platform) uses 3MF as the preferred format and surfaces embedded print settings from 3MF project files to prospective downloaders.
The migration is incomplete: Thingiverse still has overwhelmingly more STL files than 3MF, and Grabcad and MyMiniFactory lean heavily on STL. For any new model upload, 3MF is the better choice in 2026; for consuming existing models, STL will remain common for years. Slicers handle both transparently, so there's no practical barrier to using the formats interchangeably at import.
Should You Switch?
For new design work: yes. Any CAD tool that exports 3MF (Fusion 360, Onshape, SolidWorks, FreeCAD) should be configured to use it as the default export for printing. For slicer project saves: use 3MF exclusively — the information preservation justifies the marginal file size increase over STL. For sharing designs: 3MF for anything with color, multi-material, or orientation context; STL is acceptable for simple single-body single-color models where none of that metadata matters.
3MF and Print Farm Workflows
For print farm operations — multiple printers running from a common job queue — 3MF's embedded print settings are particularly valuable. A 3MF project file authored by a designer can contain the complete slice configuration (layer height, wall count, infill, supports) alongside the geometry, allowing farm operators to receive job files and print them without configuration overhead per job. This is only possible because 3MF supports structured metadata that STL cannot carry. Bambu's Farm Management System and Mosaic's Palette products both use 3MF as the transport format for this reason.
The material extension specification in 3MF allows encoding the intended material and color for each body in a multi-material assembly. When a slicer with AMS or MMU support opens a properly authored 3MF, it can automatically assign materials to printer inputs based on the embedded color data. Workflows that automate multi-material job setup — reducing the per-job configuration to verifying assignments rather than setting them — depend on this capability. It's another dimension of 3MF's advantage that becomes visible only at scale but is architecturally clean even for single-printer hobbyist use.
