Origami, art of folding paper to create three-dimensional figures of animals, people, objects, and abstract shapes. Origami is a Japanese word that combines the verb oru (to fold) and the noun kami (paper). The only material required for origami is a piece of paper. Almost any paper may be used, but folding is easiest if the paper is thin, strong, and able to hold a crease. Standard origami paper is usually cut into 15-cm (6-in) squares; it is generally plain white on one side, with a color or decorative pattern on the other. Some origami artists experiment with other materials, including cardboard, cloth, wire mesh, sheet metal, and even pasta. To fold origami, a person only needs to learn a few standard types of folds. These folds are used to form bases, or starting shapes, for different figures. The four most common bases are the kite base, the fish base, the bird base, and the frog base. To these bases, paper folders add additional folds to create figures of virtually any shape, including animals, insects, people, plants, vehicles, and buildings. Some paper folders specialize in abstract shapes, while others focus on modular origami, making multiple copies of a single, simple shape and assembling these pieces into elaborate structures. The origin of origami is unclear. Some historians argue that paper folding began soon after Cai Lun (Ts'ai Lun) of China invented paper in AD 105, and that when Buddhist monks introduced paper to Japan in the early 7th century, they brought paper folding along. However, other historians claim that origami is a Japanese invention. They point out that there are no known Chinese records of early paper folding, and that Japanese records of the practice only date from the 18th century. Regardless of origami's origins, its practice was most fully developed in Japan. Origami, and paper itself, were so highly valued in Japan that certain origami models became part of religious ceremonies.