What is an STL file? What does .STL stand for? How do you edit or fix an STL file? Here’s your introduction to the STL file and how it’s used with 3D printing.

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What is a .STL File?

A STL ( file is a  file format most commonly used in additive manufacturing/3d printing.  Essentially, it’s mesh of triangles that represent a 3D CAD model.

The triangles link together to represent the surface geometry of the model. Each triangle facet has perpendicular direction and three points that connect to form the surface features of the model. The data contained in the STL file is a full log of the X, Y and Z coordinates of the triangle points, and their perpendicular position.


What does STL stand for?

While originally it was an abbreviation for STereoLithography , STL is now widely referred to as “Standard Tessellation Language” or “Standard Triangle Language”.


What are the common issues with the STL file format?

There are no units specified within a STL file, which can result in scaling issues when a file is uploaded to be quoted where the model appears to be abnormally sized.Millimeters is the most common unit. Another major issues is that the triangle mesh is frustrating to edit, particularly when surfaces are overlapped or inverted.

The data within an STL file only describes the surfaces of a model. Information about color, texture, or material is not included, which leads to complications  when printing in a process like Polyjet.In addition, because smooth, curved surfaces require so many triangles to represent them, file sizes for these types of geometries can be huge.

The STL format is considered outdated by many, as the types of files being produced now are much more complex than the STL was designed to handle. We now have the ability to print in multiple materials, in full color, and with extremely fine resolution; characteristics that the STL simply cannot handle.

Fortunately, there are new file formats on the horizon. With the release of HP’s new 3D printer in 2017,  we could control color, translucency, material and texture by adjusting the nature of each 3 dimensional pixel, known as the voxel.

What are the advantages of the STL file format?

For all its faults an STL file is simple and straightforward. Even the most complex geometries can be reduced to lines and surfaces.

In addition, it’s been the standard file format for so long that users can export one from almost any CAD modeling software. There’s been a large investment into the file format over the years by large companies in the 3D printing industry, software companies, and users who share and download files on the internet.  

Furthermore, the growing software & service market for editing and repairing the STL files has made it easier to prepare files for 3D printing. So many people have become accustom to it and invested development time into it that the STL has remained the standard.

How do you edit or convert an STL file?

There are a number of tools that allow you to edit STL files. Blender, Meshmixer and MeshLab are some of the most popular.

Meshmixer- is a free software project from Autodesk that allows you to edit STL meshes. You can hollow, thicken, cut and perform advanced edits.

Meshlab - is great for quick polygon reduction to reduce file size. It allows for the import & export of a wide variety of files types, not just STL.

Blender (advanced users) is a free, open source 3D graphics and rendering software the allows for the creation and editing of 3D models.

How do you repair a broken STL file?

Other related questions: How do I increase the wall thickness of my model? How do I make my model watertight/manifold? How do I fix overlapping objects? How do I separate shells i meshmixer?

There are a number of reasons why  an STL file can be unprintable. See our guidelines for some common problems with 3D models.

The tools below can help you fix issues you encounter such as inverted surfaces or wall thickness issues:


Netfabb (free)

  • This tutorial will help you clean up and fix your STL files for 3D printing
  • This walkthrough shows how to do basic STL repairs automatically with Netfabb

Materialise Cloud (paid)


How do you create a STL file?


STL files are exported from CAD programs such as Solidworks or ProE. 

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