MATERIAL- 28 Liters. This military backpack is made of 600D Water resistant Polyester. YKK Zipper. HYDRATION COMPARTMENT- This assault pack with hydration compartment and can hold a 2 Liter bladder , the tube is fed through the top of the bag near grab handle. MOLLE WEBBING- This rucksack can hang on small items, or for attaching additional pouches or gear. Backpack also has 2 adjustable straps underneath to attach a bedroll, tent or anything else. Side mesh pocket fits water bottle.