File with an .MTL extension contains text information on texture patterns used in adequate objects (OBJ file). It sores information on bitmap names and their location within a project and distribution on a 3D object.

MTL setting files are utilised by 3D modelling software in order to save material settings. Due to the fact that they are test files, they can be opened and modified in regular text editors, however, it is not advised because it may result in disruption of relations within a project.