A material library is a collection of materials and related assets. Some libraries are provided by Autodesk, and others are created by users. You can create libraries to organize your materials. You can also share libraries with other people on your team, and use the same libraries with Autodesk Inventor and Revit to support the use of consistent materials.
The libraries supplied by Autodesk are locked, as indicated by a lock icon. Materials in a locked library cannot be overwritten or deleted. You can copy materials from a locked library to unlocked user-created libraries, where materials can be overwritten or deleted. In the figure, Favorites, My Materials, and AB Project Materials are unlocked user-created libraries.
Libraries can be sub-divided by adding categories and moving materials into the categories. An Autodesk-supplied library contains many categories of materials organized by type, such as Concrete, Metal, and Glass. User-created libraries and categories can reflect different methods of organization, such as project names or usage. In the figure, the AB Project Materials library contains a Construction category.
To work with libraries, use the Material control to open the Material Browser.

Material Browser
To add a material to the current document, first find the material in an existing library, then use one of these methods:

To copy a material to a library, use one of these methods:
If you copy a material to a library where another material of the same name exists, you are prompted either to overwrite the version in the target location or to keep both.