There is only one file type that uses the .MTL extension:
OBJ Material Template Library File
An MTL file is a material settings file used by 3D object editing applications, such as Adobe Photoshop and Autodesk Maya. It is stored alongside an .OBJ file and describes how a program should apply textures to that object. MTL files contain the names of the texture bitmap files to apply to an object as well as the 3D coordinates at which to apply them.
Because MTL files are saved in plain text format, you can open an MTL file in any text editor, including:
- Notepad (Windows)
- TextEdit (Mac)
NOTE: Because they are text files, you cannot open MTL files in 3D object editing applications such as Adobe Photoshop and Autodesk Maya (even though those applications create MTL files). These applications reference and apply settings from MTL files when you open a corresponding OBJ file.
Updated: March 10, 2020