A frame is an outer border, usually made of wood, wood composite, resin or metal, which encloses and binds together a picture in its mat, often under glass. A particular style of frame is called a frame moulding. Wire for hanging the picture on the wall is attached to the stable material of the frame. Thus, the frame serves several important functions. It enhances the appearance of the artwork, provides a support for attaching it to the wall or other display surface, and also helps protect it, should it be dropped or should dust or other pollutants accumulate on the surface.