Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In geometry the net of a polyhedron is an arrangement of edge-joined polygons in the plane which can be folded (along edges) to become the faces of the polyhedron. Polyhedral nets are a useful aid to the study of polyhedra and solid geometry in general, as they allow for models of polyhedra to be constructed from material such as thin cardboard. It is a long-standing open question whether or not every convex polyhedron P (one without "dents" in other words, all dihedral angles between the edges are 180 degrees) has a net: whether the surface P may be cut along edges and unfolded flat to a planar polygon (without overlap).