This Double Breast Developer Pump system features twin breast sucking cups and (this is the big difference between this breast enlargement system and others) twin pressure release valves, this means you can adjust the pressure for each breast, (ideal for differently sized boobs). The double breast developer pump has a hand pump that provides the vacuum which will make the breasts grow naturally. Providing breast enlargement for every cup size. Elasticated neck and back straps are fully adjustable just like a bra.