The 31" Zipsak is an extra large 4-wheeled duffel that folds into a small. easy-to-store pouch. Ideal for longer trips. college. summer camp and ski trips. the 31" Zipsak packs a ton. and then stores away neatly until you're ready to hit the road again! Its dual-opening packing system features a large wrap around zippered opening. plus an easy access top zippered opening. Made from a durable nylon fabric. the Zipsak is tear-proof. water resistant. and ultra lightweight.