The design of the Twenty mirror is based on a geometric body, the icosahedron (polyhedron with 20 faces) in its most popular form, the regular convex . The different faces are created by changing the thickness of the lines printed on the back of the mirror glass: although they are in one colour, this optical illusion gives one face a seemingly darker colour than the other, thus creating a shadow effect. Only the central part is a plain mirror and can be used as such.