3MF File Format

3MF is a ZIP-based 3D manufacturing format that can package triangle meshes, build placements, unit declarations and optional appearance data in one model file.

What the 3MF format contains

A 3MF file is an archive rather than a plain list of triangles. A typical package contains a model document with resources and a build section. Resources can define mesh objects and component assemblies; build items place those objects in the scene. Other package parts can hold materials, colors, textures, thumbnails and related metadata.

This organization lets one file describe more than a bare surface. It can express a unit, object references and placements, and some formats can describe appearance. The exact information depends on the model and the features implemented by the application that created or reads it. Not every 3MF file uses every feature.

3MF compared with STL

STL is a triangle surface format with broad support in slicers and modeling software. It has no standard unit field, assembly hierarchy, texture coordinates or general material model. 3MF can store declared units and package additional model information alongside its mesh, but it is not native parametric CAD and does not preserve the original feature history of a design.

When converting 3MF to STL, placements and unit scaling can be applied to the output triangle coordinates, but STL cannot retain the 3MF unit declaration, object identities or appearance data. A converter should report these losses and verify the resulting geometry rather than implying that the two formats contain identical metadata.

Units and dimensions

A 3MF model can declare microns, millimetres, centimetres, inches, feet or metres. The unit scales vertex coordinates and placement translations together. If a model omits the unit attribute, the format defines a millimetre default; software should say that it applied this default rather than presenting it as a unit declared by the file.

STL coordinates are unitless. A 3MF made from STL can declare millimetres, but that declaration is an assumption about the input coordinate values, not information recovered from STL. Always compare the displayed bounds with a known dimension before manufacturing or sharing the model.

Objects, components and build placements

A 3MF package can define a mesh once and reference it from one or more build items. A component object can group other objects, and transforms position or rotate each reference. A reader must apply the full transform chain to report the visible scene bounds. Counting XML mesh resources alone can overcount unused meshes or undercount repeated instances.

STL does not define a standard assembly tree. A 3MF-to-STL workflow can write each placed mesh as a separate solid group and report object counts, but applications may flatten the file later. Conversely, an STL-to-3MF converter usually creates one geometry object because STL does not reliably identify its original objects.

Appearance and compatibility

3MF may include base colors, material groups, textures or other appearance resources. Viewer support varies by application and by feature profile; some specialized extensions may not render everywhere. STL cannot retain that appearance information. Keep the original 3MF when colors or textures matter, and verify imported results in the target software.

A file extension alone does not prove that a package is valid. The model should contain a readable model part, valid mesh references and a usable build section. External references and malformed or unsafe archive entries can prevent reliable reading. Large compressed packages also need limits on expanded data and triangle count.

View or convert a 3MF model

The browser-based 3MF viewer reads a local file on your device, displays its geometry and reports build items and unit scaling. A missing unit is surfaced as the specification default of millimetres. The viewer does not send the model to the conversion server, and the actual available appearance features depend on the file and browser loader.

For a verified mesh output, use the 3MF to STL converter. It applies supported placements and scales declared units to millimetres, then compares the saved STL with the source. For an STL source, the reverse converter creates a one-object 3MF with an explicit millimetre unit and reports that the original STL had no unit metadata.

Frequently asked questions