.STL File Extension

Stereolithography File

Developer 3D Systems
3.7  |  89 Votes

What is an STL file?

An STL file is a 3D model saved in the Stereolithography (STL) file format developed by 3D Systems. It contains plain text or binary data that describes a set of triangular facets, which comprise a model. STL files are quite common, and they can be opened in many CAD and 3D modeling programs.

More Information

Screenshot of a .stl file in Microsoft 3D Viewer
STL file open in Microsoft 3D Viewer

Stereolithography is a form of 3D printing primarily used for creating product prototypes. In the late 1980s, 3D Systems co-founder Chuck Hull patented stereolithography technology, and 3D Systems created the STL file format. Primarily, STL files contain 3D models meant to be printed using stereolithography.

Because the STL format was one of the first formats used to store models for 3D printing, a large number of 3D model viewers and CAD programs support it. STL files may be saved as plain text files, which contain human-readable triangular tessellation data, or as binary files, which contain the same data saved in a binary format. When opened in a text editor, plain text STL files appear as a list of facets and vertexes, complete with coordinates. These files always begin with the string solid ModelName.

NOTE: STL files are also sometimes referred to as Standard Triangle Language files and Standard Tessellation Language files.

How to open an STL file

Plain text STL file open in Apple TextEdit
Plain text STL file open in Apple TextEdit

You can open an STL file in many image viewers, 3D modeling, and CAD programs, including:

You can also open plain text STL files in text editors, such as Microsoft Notepad and Apple TextEdit, to view the plain text data they contain. (If you open a binary STL file in a text editor, its data will appear as a series of unintelligible characters.)

How to convert an STL file

Several CAD and 3D model editing programs, including Autodesk Fusion 360 and Microsoft 3D Builder, can convert STL files to other 3D model formats. For example, Fusion 360 can export STL files to:

  • .F3D - Fusion 360 Archive
  • .3MF - 3D Manufacturing File
  • .IPT - Inventor Part
  • .FBX - Autodesk FBX Interchange File
  • .OBJ - Wavefront 3D Object
  • .SKP - SketchUp Document
  • .SMT - Autodesk Shape Manager Text File
  • .STP - STEP 3D Model
  • .USDZ - Universal Scene Description Zipped

Apple Preview and Microsoft 3D Viewer can convert STL files to raster images. For example, Microsoft 3D Viewer can convert an STL file to the following formats:

  • .PNG - Portable Network Graphic
  • .JPEG -JPEG Image
  • .BMP - Bitmap Image
  • .TIFF - Tagged Image File Format

Apple Preview can also convert STL files to .PDF documents.

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Programs that open STL files

Category: CAD Files
Updated: December 22, 2022

Certificate Trust List

Developer Microsoft
2.8  |  13 Votes

List of predefined items that have been signed by a trusted entity; may consist of a list of filenames or a list of certificates; each item in the list has been approved by the signing entity.

More Information

Certificate trust lists (CTLs) are used by Microsoft IIS to store trusted websites and other addresses that require a secure connection.

Programs that open or reference STL files

SuperTux Level File

Developer SuperTux
2.7  |  10 Votes

Game file used by SuperTux, a 2D jump and run side scrolling game similar to Super Mario Bros.; saved in a plain text format and specifies the features of a level, such as enemy unit locations, positions of blocks, and the time limit; also includes a reference to the music and background image for the level.

More Information

STL files are stored in the /​data/​levels/​ directory of the installation.

Programs that open or reference STL files


Fireworks Style Library

Developer Adobe Systems
2.4  |  12 Votes

Library of styles referenced by Macromedia (now Adobe) Fireworks; may be used to apply Stroke, Fill, Effect, and Text attributes to an object within an open Fireworks project; can be helpful for creating a uniform look across multiple objects.

More Information

Some styles are included with Fireworks, though additional styles may be added to the program. To add extra styles, click the small icon in the top right corner of the Styles panel in Fireworks and select "Import Styles." Then browse to an STL file and click OK to add the style library to your current collection.

Programs that open or reference STL files

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European Broadcasting Union Subtitles File

Developer European Broadcasting Union
2.2  |  12 Votes

An STL file may also be a subtitles file saved in the European Broadcasting Union (EBU) subtitle data exchange format. It contains binary data used to load subtitles and store subtitle metadata. STL files are used mostly to provide subtitles during TV broadcasts.

More Information

In 1991, the EBU published specifications for the STL subtitles format. STL files contain a set of subtitle texts and information, such as time codes and positioning, used to display that text during a broadcast. The files also contain metadata that defines the subtitles' publisher, editor, and country of origin.

Unlike many other types of subtitle files, STL files are binary files, so you cannot view or edit the text they contain in a text editor. Some broadcasters still use the STL format, but the format has largely been replaced by the newer, XML-based EBU-TT format.

How to open an STL file

You can open an STL file with EZTitles (Windows) or Avid Media Composer (Windows, Mac). These programs allow you to import STL files and use them as subtitle tracks while creating a video. You can also view the subtitles and metadata an STL file contains with Jongbel Media Solutions EBU STL Viewer (Windows).

How to convert an STL file

You can use Jongbel Media Solutions EBU STL Viewer (Windows) or EZConvert (Windows) to convert STL files to many other subtitle formats, including:

  • .SRT - SubRip Subtitles
  • .ASS - Aegisub Advanced SubStation Alpha
  • .PAC - PAC Subtitles
  • .VTT - Web Video Text Tracks
  • .SUB - MicroDVD Subtitles
  • .890 - Cavena Subtitles
  • .USF - Universal Subtitles Format

Programs that open STL files


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