A breast implant is a sac of silicone rubber that is implanted under your chest tissue through surgery. This sac is either filled with silicone gel or saline solution.
The silicone gel, a soft, solid substance, is more commonly used in breast implants.
The saline breast implant is inflated with a saline solution through a valve. Saline, or salt water, is actually similar to the fluid that makes up the human body, and there are two ways of putting saline in an implant. One has a self-sealing valve located on the front part of the implant that is used for filling the sac with saline. The other one has a valve on the back of the implant that allows saline to be added post-surgically, enabling your doctor to adjust the size of your breasts afterwards. In this second type of saline-filled implants, your doctor can change its size by either adding or removing saline for up to six months after your surgery.