An awning or overhang is a secondary covering attached to the exterior wall of a building. It is typically composed of canvas woven of acrylic, cotton or polyester yarn, or vinyl laminated to polyester fabric that is stretched tightly over a light structure of aluminium, iron or steel, possibly wood or transparent material (used to cover solar thermal panels in the summer, but that must allow as much light as possible in the winter). The configuration of this structure is something of a truss, space frame or planar frame.