Breast prostheses are breast forms intended to simulate breasts. There are a number of materials and designs. The most common construction is silicone gel in a plastic skin.
Many pre-op and non-op transwomen and males who cross-dress as females use breast prostheses in order to create the illusion of feminine breasts. They are sometimes combined with cleavage enhancement techniques when used with clothing with low necklines.
Different shapes of prostheses are used to suit the extent of breast tissue removal or the shape of a crossdresser's chest. Asymmetric breast forms incorporate an extension towards the armpit to replicate the shape of the tail of Spence, while symmetric, "triangle" or "teardrop", prostheses do not incorporate that extension.