There are a few goals for 3MF. One is to have a common format that is portable across tools made by the big companies participating in the consortium. Another i

There are a few goals for 3MF. One is to have a common format that is portable across tools made by the big companies participating in the consortium. Another is support for specifying material in addition to shape. STL can represent a part, but can’t distinguish it as a specific metal or plastic. STL also can’t specify color. Those properties can be used in engineering software to simplify analysis and visualization. 3MF also supports multiple parts, which is useful in a multi-material build. For example, when a dentist 3D prints a mouth model they might use white for the teeth, red for the jaws, and a removable support material. With STL each of those sub-models would be a separate file, meaning the 3D printer operator would need to properly position them and choose appropriate materials at build time.