Kimono are usually made of silk, but there are cotton, polyester, hemp and linen kimono as well. Some kimono are also made of wool, or rayon. Formal kimono are always made out of fine silk, and are usually sewn by hand. However, not all silk kimono are formal kimono, and some types of silk, such as pongee (known as "tsumugi") are only ever worn to casual occasions.