The tyMtlLib material automatically loads a material from a .mat file, for simple material referencing. Changes to a .mat file will automatically propagate to any tyMtlLib materials, when a max file is reloaded, or the “reload” button is pressed in the tyMtlLib UI. The tyMtlLib functionality is similar to that of the built-in XRefMaterial, however loading/referencing materials directly from a .mat can be more convenient than loading/referencing them from an XRef.
The chosen index will be internally clamped to the range of available materials in the .mat file.