Obi (帯?, おび) is a sash for traditional Japanese dress, keikogi (uniforms for Japanese martial arts), and part of kimono outfits. The obi for men's kimono is rather narrow, 10 centimetres (3.9 in) wide at most, but a woman's formal obi can be 30 centimetres (12 in) wide and more than 4 metres (13 ft) long. Nowadays, a woman's wide and decorative obi does not keep the kimono closed; this is done by different undersashes and ribbons worn underneath the obi. The obi itself often requires the use of stiffeners and ribbons for definition of shape and decoration. There are many types of obi, most for women: wide obi made of brocade and narrower, simpler obi for everyday wear. The fanciest and most colourful obi are for young unmarried women. The contemporary women's obi is a very conspicuous accessory, sometimes even more so than the kimono robe itself. A fine formal obi might cost more than the rest of the entire outfit. Obi are categorised by their design, formality, material, and use. Informal obi are narrower and shorter.