STL (STereoLithography): Format for Printable 3D Files

STL is a 3D file format. It is used to store uncolored mesh. It was initially developed by 3D Systems.

STL file
A triangular mesh as stored in an STL file

Information about Storage

  • An STL file describes mesh surfaces as lists of geometric features. A solid is composed of triangular faces, which are composed of a normal and 3 vertices described by their coordinates. 
  • The normal is optional and can be used to determine the inside of the mesh. In case normals are not properly set they can be computed using the face vertices. If it is not possible to determine the inside of a mesh, it must be repaired . 
  • Information can be stored either in plain text or binary form, the later is used more often as it is a more efficient storage. 
  • Vertex position are saved without any unit. The unit can be set on Sculpteo website after it is uploaded. 

Description of the STL file format

Here is a non-exhaustive list of software supporting STL.

Direct file exports:

Exports after tessellation:

Tessellation is the phase used, where the geometry is transformed into triangles in order to be saved. This phase may alter the original mesh if the resolution is too big. 

Difference between original surface and tessellated surface

When to use STL Format


  • Compact and simple file format. The file format only specify the bare minimum to describe 3D model which makes it easy to use. Like other mesh file format (obj, wrl, ply, …) there is no need to go through a tessellation phase which alters the original mesh to obtain a printable file. 
  • Supported by multiple 3D modeling softwares and 3D  printers .


  • Discards connectivity information, but most 3D softwares can infer it, Sculpteo tools will recompute it when the model is uploaded. 
  • Color support is not standard and often not supported. for multicolored mesh you must choose another format from this list .

STL files are good choice to upload a single color model on Sculpteo website as the color can be chosen afterwards.