Description of Sea to Summit Ultra-Sil Pack Liner Sea to Summit also has a “pack liner” made of the amazingly light Ultra-Sil. The shape of the sack is designed to fit the internal contours of a backpack, so the base is oval, rather than round. Features: Ultra-Sil Pack Liner opens wide for easy packing when it’s inside a pack Unique top closure: extra fabric at the top folds in and velcros in place, then rolls down, creating a more compact closed loop at the top Made of PU coated Siliconized Cordura® Huge waterhead Non-wicking Hypalon™ roll-top closure with stiffener at the top for a better seal Fully seam sealed Uses low profile buckles Slippery finish for easy packing Three sizes available to fit different pack volumes Comes assorted in three cool new colors: kiwi green, baby blue and orange orange