This super heavy duty dry bag is specifically designed to perform in extreme conditions where toughness and abrasion resistance are required. The Hydraulic is made from 600D TPU laminated fabric with a completely welded construction for durable waterproof seams and a snag-free seam profile. The fabric is PVC-free and UV resistant. It sheds water and does not crack in extreme cold. 600D Hydraulic FabricThe fabric the Hydraulic dry bags are made from is stiffer and tougher than Sea to Summit's Stopper fabric. It is constructed from a 300D x 600D Nylon with a heavy TPU laminate exterior. The 600D X 300D is the best strength to weight fabric in this category, and the heavy TPU laminate gives a tough, smooth, water-shedding exterior and allows Sea to Summit to weld Hydraulic Dry Bags, meaning no sewing or taping is required. This is the guide/expedition grade dry bag fabric. Sea to Summit's Hydrostatic test machine couldn’t find the water-proof limits of this fabric, and they got bored with trying to abrasion test the fabric to destruction.