Kimonos are worn with wide belts called Obi. The Obi holds the overlapping kimono in place, and keeps the front closed. The Obi has as much importance as the kimono itself. Tying the Obi into a knot and a perfect bow in the rear is a difficult art to master. Women usually seek the services of a professional. There are two main types of Obis, a formal and a casual. The formal Obi is usually 4 meters long and 60 centimeters wide. It is folded in half lengthwise, wrapped twice around the waist and then tied in the back. Formal Obi belts are made of a silk brocade or woven tapestry. Woven or embroidered designs in gold or silver are also common. The more complex designs are considered more formal. The casual Obi is often narrower and made of cheaper fabric such as satin, twill, cotton, nylon or wool. It does not have the elaborate silk brocade embroidered patterns found on formal belts.