A file format used in most additive manufacturing processes. It is a faceted representation of the geometry that is easy to slice. The format was developed for stereolithography but is used across technologies.

The format is either ASCII or Binary and contains a list of triangles that define the outside surface of an object.

For the ASCII Format, Each object is defined as:

solid name
... facet...
endsolid name

For each triangle, the following information is included:

facet normal x y z
  outer loop
    vertex x y z
    vertex x y z
    vertex x y z

Where “x y z” are real numbers separated by space or tabs, defining the normal vector or location of each vertex. This information is encoded as 32-bit floating-point numbers with a  header for binary.

By default, the format does not contain additional information, like color or curvature, but some vendors have added header information to include additional details about the objects.

The format is being deprecated and replaced by 3MF.

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