 While most mats are generally rectangular in shape, with a rectangular opening, in addition to fairly common oval, oval-apertured mats designed to go with oval frames, there are also very unusual examples of mats in other shapes.Mats are, with very few exceptions, made of paper-based material.They tend to take well to minor surface additions, including ink and paint (a very wide variety of other media, including fumage, have been used); cloth-covered mats can also have objects such as pins, flags or cloth patches pinned or sewn to them, a technique frequently used in shadowboxing to avoid having to glue items to the backing.