Breast implants are small, medical-grade sacs comprised of an elastomer shell with a self-sealing filling valve located on either the front or back. Breast implants are filled with silicone gel or a sterile saline solution (salt water).
Some implants are pre-filled, but most are filled after surgery. It's this filling that blows the implant up like a water balloon to increase breast size. Saline implants are the most common type of implant used today due to the FDA's ban on the use of silicone breast implants in the United States in 1992 (although silicone implants are still available in certain circumstances -- see the Controversy section).
Breast implants come in a variety of shapes and sizes. The size of breast implants is measured in cubic centimeters (ccs), and they increase the size of a woman's breasts one cup size every 175 to 200 ccs.
Generally, implants come in three sizes, and the size of the implant that is used depends on the patient's desired outcome and the size breasts that their physical frame can support. Choosing a breast implant that is too large can cause surgical complications or make the implant visible through the skin after the surgery.
In the next section, we'll look at some of the special features of breast implants.