It's easy to view the contents inside Sea to Summit's 20 L Ultra Sil View Dry Sack with its strong, RF welded, clear TPU window. Ultra Sil 30D siliconized high tenacity Cordura nylon fabric for exceptional strength. Ultra Sil fabric has a 2,000 mm waterhead. Siliconized fabric for extra strength, durability, and a smooth finish for easy packing supercompact and ultralightweight. Hypalon roll top closure does not wick moisture. Polyurethane coated and fully seam sealed for ultimate waterproofness when bag is not submerged. TPU window is RF welded into side panels for a bond as strong as the materials being used. Reinforced stitching for greater seam strength on all stress points. Round base design in all sizes. Suitable to keep contents dry in any wet situation where the bag is not submerged.