Kozo

Kozo refers to the fiber derived from the inner bark of the paper mulberry tree, chiefly Broussonetia papyrifera. In traditional East Asian papermaking, kozo fibers are a primary component of washi, a durable and flexible paper. The term derives from Japanese usage for the tree and its fiber.

Botanical background: The paper mulberry is a fast-growing deciduous tree native to East Asia and widely cultivated for fiber. Its bast fibers, long and strong, are harvested from the inner bark and processed into pulp for papermaking. Related species such as Broussonetia kazinoki may also be used.

Production: Bark is harvested and the outer bark removed, then retted, washed, and beaten to separate fibers. The kozo pulp is formed into sheets on a mold or screen and air-dried. In traditional practice, kozo is often blended with other fibers, such as mitsumata or gampi, to achieve a range of textures and strengths.

Uses and properties: Kozo fibers yield high-strength, long-lasting papers with excellent surface quality and absorbency. They are highly valued in art papers, conservation-grade papers, and bookmaking, as well as in calligraphy and crafts. Papers made from kozo age well, developing a distinctive patina.

Modern context and considerations: Kozo remains central to traditional washi production in Japan and is produced in other parts of Asia and beyond. Environmental considerations include sustainable harvesting and management of non-native plantings, as Broussonetia papyrifera can naturalize in some regions.