There are a few ways to distinguish between natural breasts and those with implants. Implants may feel firmer to the touch, and their shape may be more rounded or symmetrical than natural breasts. In addition, the movement and appearance of breasts with implants may be different, especially when lying down or during physical activity. However, advances in surgical techniques and implant materials have made it increasingly difficult to tell the difference between natural breasts and those with saline or silicone implants.