The original Fat Sac redefined. The new Pro X Series Fat Sacs are constructed with a white water rafting material called Valmex. These sacs are unbelievably durable and no longer need the support of an outer shell. They also come equipped with our Quick Connect Valve system making filling and draining these things an easy task. Furthermore, the placement of our valves makes it possible to daisy-chain them to create the perfect integrated ballast system. Available in assorted colors.