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Japanese paper traditionally made from mulberry tree bark

Washi (和紙) is traditional Japanese paper processed by hand using fibers from the inner bark of the gampi tree, the mitsumata shrub (Edgeworthia chrysantha), or the paper mulberry (kōzo) bush. Washi is generally tougher than ordinary paper made from wood pulp, and is used in many traditional arts. Origami, shodō, and ukiyo e were all produced using washi. Washi was also used to make various everyday goods like clothes, household goods, and toys, as well as vestments and ritual objects for Shinto priests and statues of Buddha. It was even used to make wreaths that were given to winners in the 1998 Winter Paralympics. Washi is also used to repair historically valuable cultural properties, paintings, and books at museums and libraries around the world, such as the Louvre and the Vatican Museums, because of its thinness, pliability, durability over 1000 years because of its low impurities, and high workability to remove it cleanly with moisture. As a Japanese craft, it is registered as a UNESCO intangible cultural heritage.

By the 7th century, paper had been introduced to Japan from China via the Korean Peninsula, and the Japanese developed washi by improving the method of making paper in the Heian period. The paper making technique developed in Japan around 805 to 809 was called nagashi suki (流し漉き), a method of adding mucilage to the process of the conventional tame suki (溜め漉き) technique to form a stronger layer of paper fibers. The improved washi came to be used to decorate religious ceremonies such as gohei, ōnusa (:ja:大麻 (神道)), and shide at Shinto shrines, During the Edo period, many books and ukiyo e prints for the masses made of washi were published using woodblock printing.

Washi is produced in a way similar to that of ordinary paper, but relies heavily on manual methods. It involves a long and intricate process that is often undertaken in the cold weather of winter, as pure, cold running water is essential to the production of washi. Cold inhibits bacteria, preventing the decomposition of the fibres. Cold also makes the fibres contract, producing a crisp feel to the paper. It is traditionally the winter work of farmers, a task that supplemented a farmer's income. Paper mulberry is the most commonly used fiber in making Japanese paper. The mulberry branches are boiled and stripped of their outer bark, and then dried. The fibers are then boiled with lye to remove the starch, fat and tannin, and then placed in running water to remove the spent lye. The fibers are then bleached (either with chemicals or naturally, by placing it in a protected area of a stream) and any remaining impurities in the fibers are picked out by hand. The product is laid on a rock or board and beaten. Wet balls of pulp are mixed in a vat with water and a formation aid to help keep the long fibers spread evenly. This is traditionally neri, which is a mucilaginous material made from the roots of the tororo aoi plant, or PEO, polyethylene oxide. One of two traditional methods of paper making (nagashi zuki or tame zuki) is employed. In both methods, pulp is scooped onto a screen and shaken to spread the fibers evenly. Nagashi zuki (which uses neri in the vat) produces a thinner paper, while tame zuki (which does not use neri) produces a thicker paper.

With enough processing, almost any grass or tree can be made into a washi. Gampi, mitsumata, and paper mulberry are three popular sources.