Sea to Summit Pack Covers are durable, lightweight, contoured to fit today's packs, and pack away into a compact stuff sack when not in use...so there's really no reason why you should ever hike without one.. . Made of 70D polyurethane coated nylon for long lasting durability. 2,000 mm waterproof fabric ensures that your pack and its contents stay dry. All seams are tape sealed for added waterproofness. Cover is contoured to better fit modern packs. Packs away into its stuff sack included for easy storage when not in use. Made for 20 30 L 1220 1800 cu. in. packs.