Description of Sea to Summit Ultra-Sil Dry Sacks The new Sea to Summit Ultra-Sil™ Dry Sacks are more than 50% lighter than our super popular Dry Sacks. They’re made of Siliconized Cordura®, which is one of the lightest and toughest waterproof nylon fabrics available. Now you don’t have to choose between keeping your gear dry and keeping it light. Features: Super compact and ultra lightweight Made of Ultra-Sil™ nylon, a polyurethane coated Siliconized Cordura® for ultimate waterproofing and maximum durability Watertight, non-wicking Hypalon® roll top closure with stiffener at the top for a better seal Soft and flexible with a slippery finish for easy packing Nearly transparent allowing good visibility of the contents All seams are double stitched and tape sealed Smaller sizes have flat bottoms, others are round