As a zipped XML package, 3MF is generally smaller (often significantly) than other comparable 3D formats. Transforms and object references are supported, with multiple objects contained within the single archive. Single objects can be referenced or moved without changing the mesh, and multiple identical objects can be placed referencing the same mesh.
3MF provides a clear definition of manifoldness and open source code is available for rapid validation. The strictly positive fill rule specifies the exact interpretation of any model with self-intersections or overlaps. Likewise, color and property interactions are clearly specified so that the end result is the same for any conforming implementation of 3MF.
The 3MF consortium maintains a cross-platform open source library for reading, writing and validating 3MF files, which also contains sample objects and test cases. Microsoft has also made APIs available in Windows 10 for reading, writing, validating, repairing and simplifying 3MF files, and 3MF is also used as the format to submit 3D print jobs to the print pipeline.
There is no need, since anyone can use and extend 3MF without joining. The consortium does not plan to add any more founding members, as the industry is already well represented and keeping the group small keeps the pace of innovation up, which is why we are not moving into a standards body yet. The 3MF associates program offers members early access to specifications in progress, but has cost in both money and in giving up related IP.
3MF is focused on additive manufacturing; it can be used with CNC or laser cutters, but the consortium is not putting effort into supporting the nuances of those processes as they seem to be reasonably well-served by existing formats (CNC by IGES and STEP, laser by DXF and PDF).
STL does not contain color or other material/property information, and has no extensibility mechanism to add it. STL does not save mesh topology, leading to larger file size, loss of manifoldness due to rounding errors, resulting in ambiguity. 3MF solves all of these problems.
AMF inspired the foundations of 3MF, but AMF is widely held to have gone into a standards body too early, having some features not clearly defined and other features missing. The 3MF consortium was formed to bring the industry leaders together to agree on a format that would serve the industry’s needs.
The rendering formats are not designed for manufacturing: they have a lot of information on rendering effects such as lighting and fog, but are missing true material properties and their implementations are often inconsistent. 3MF is designed to contain their geometry and color data without translation loss, while narrowing the scope to avoid shaders and other unnecessary complexity.
3MF is not intended to compete in the CAD space, as it does not and will not support higher-order representations such as NURBS. However, it will be a useful export format for these systems by creating unambiguous geometry for manufacturing that can be read more universally, as 3MF is designed to be much simpler to implement than the full CAD formats.
3MF is geometry focused and has no intention of building in the kind of complexity necessary to represent manufacturing process and instructions. The simplicity of 3MF is ensured by a focus on defining what is manufactured, not how.