900D waterproof fabric, but the zipper is not waterproof 37L,External dimensions:19"(H) x 11"(W) x 11"(D),waist belt MAX:55 Inch,chest belt MAX:60 Inch 37L models Military backpack has hydration compatible that works great for a hydration bladder (backpack didn't include hydration bladder) as hydration backpack or outdoor camping hiking backpack. This tactical assault pack backpack can be used as assault pack, bug out bag backpack, range bag, hunting backpack, survival backpack, army backpack, trekking backpack or day pack for daily use