In corsetry, a bone is one of the rigid parts of a corset that forms its frame and gives it rigidity. The purpose of the boning in a corset varies slightly from era to era. Generally, the cinching/shaping properties of corsetry puts strain onto the fabric from which the corset is made. The boning supports the desired shape and prevents wrinkling of the corset fabric. Bones, and the substances used for the purpose, are generically called "boning"; however, the name likely arises from the use of whalebone in early corsets. Modern corset boning comes in two differently qualities metal and plastic. Since the turn of the 20th century, steel boning was the standard for a high quality corset. Coming in two different types flat spring steel and spiral steel. While spring steel is most preferred for being thin and flexible it only has the ability to bend in a single direction. Spiral steel is able to bend in left to right as well as front to back, which brings Botha pros and cons as it is not as stable and tends to not support larger figures. Traditionally plastic boning such as featherweight and Rigilene are considered low quality and unsupportive. New advances in plastic boning have brought about what is known in the costume and historical spheres as synthetic whalebones. It is used widely in historical reconstruction due to its similarities to traditional whalebone. It is light weight and very supportive. It also molds better to the body allowing for a much curvier shape. Purpose, history and materials The purpose of the boning in a corset varied slightly from era to era. Generally, the cinching/shaping properties of corsetry puts strain onto the fabric from which the corset is made. The boning supports the desired shape and prevents wrinkling of the corset fabric. Bones, and the substances used for the purpose, are generically called boning. The corsets of the 16th through 18th centuries (called "stays", "bodies" or "corps") were intended to mold the upper torso into a rigid cone like shape. The earliest corsets had a wooden busk placed down the center fronts of the corsets; these early busks were different from the newer, steel busks which have clasps to open and close. Corsets of the 17th and 18th centuries were most often heavily boned with little or no space between the bone channels. This was necessary to force the body