You can import two different types of material libraries: a library can be stored either as a COMSOL model file (.mph file) or as an XML file. Any COMSOL model containing materials can be imported as a material library, and conversely a material library stored in the COMSOL model format can be opened and modified in the same way as any other COMSOL model file. The XML format, in contrast, is a simplified text format that can be modified in a text editor or written by some external source of material data.