Breast augmentation surgery is an operation to increase breast size and improve the way they project.
A breast implant (prosthesis) is a shell made of medical silicone, filled with cohesive silicone gel or occasionally with saline (sterile salt water). Cohesive gel is not runny, and in case of rupture the gel component will stick to itself and remain in place.
Gel-filled prostheses have a similar feel to normal breast tissue. In thin women, however, both gel and saline implants may be felt and even seen. In thin women, the prostheses may be partially buried under the pectoral muscle to try and disguise it.
The prostheses must be centred under the nipple and the size that can be accommodated is determined by this and the size and shape of the underlying chest wall. Different shapes and configurations of implants of the same volume allow some choice but there are limits to how much enlargement can be achieved.