The original fat sac redefined and setting new standards. 350kg when filled, these sacs are the most demanded sacs on the market for their durability and ease of use. All Fly High Fat Sacs are constructed from a white water rafting material called Valmex. These sacs are unbelievably durable and do not need the support of an outer shell. The quick connect Quick Connect Valve system makes filling and draining an easy task.