In fashion, boning refers to rigid strips of material used to maintain the shape of a corset or bodice. Each strip of boning material is called a bone or a stay. The bones are sewn vertically into the fabric of a corset or bodice. Bones may also contribute to the cinching properties of a corset, depending upon its strength. Stays were historically made of whalebone, ivory, other types of bone, and wood, but today they are made primarily of steel or plastic.
The earliest types of corsets, worn from the 16th to 18th century, were designed to transform the upper torso into a very stiff, inverted cone shape. For this reason, very tough materials were used as boning, and there was little room between bones. In addition to whalebone, great cane was a popular support material in early corsets.
In the 19th century, corsets became less restrictive, and stays were often used only on the front of the corset. The first steel boning dates from around this time, and when whalebone became scarce and expensive in the latter 19th century, people looked to different materials for corsetry. Bones were sometimes made of cork, a plant fiber called Coraline, or Featherbone, made from the quills of feathers.
Throughout the late 19th and early 20th centuries, corsets became less and less complex and restrictive, and more emphasis was placed on comfort than on molding the body into a desired shape. Bones became used more to keep the fabric taut than to shape and support the torso. In the early 20th century, spiral boning was used for the first time. This type of boning is made of steel arranged in a flat spiral. It is more flexible than traditional stays, as it is able to bend in both directions, and therefore provides more gentle support.
Nowadays, it is very common to find plastic boning, as it much cheaper than the steel variety. However, steel remains the material of choice for high quality corsets. Plastic is often too flexible and can warp unattractively. It is also not suitable for tightlacing, a practice in which people use corsets to significantly modify the figure, as was common in earlier centuries. As a substitute for steel stays, cable ties may sometimes be used.