EASY SELF FILL / LEAK PROOF SEAL – Simple roll top hook and loop closure opens wide for easy fill and closes quickly and securely. Tall roll top gives a leak proof seal to keep your boat clean. FLEXIBLE FILL OPTIONS - Fill with rocks, gravel, sand, steel pellets, or whatever else you have handy. A sand/gravel mix will yield about 45 lbs per bag. Please note, these ballast bags come empty. FITS IN SMALL SPACES - Easily stows away in lockers, under seat cushions, or anywhere you've got a little empty space. Solid fill materials are more dense than water making ROC SAC great for tight spaces. A filled Roc Sac is about 14" x 12" x 3". PREMIUM DURABLE MATERIALS – Made with ultra-tough 22oz PVC coated polyester fabric (1000X1300D). Fabric is waterproof and UV resistant. Heat welded seams are strong and water tight. Built to last. VERSATILE APPLICATIONS – Great for boosting your wakesurfing wave and so much more. Anchor your jet ski, secure your tent, balance your small watercraft, or secure cantilever patio umbrellas, patio furniture, pool covers, trampolines, or almost anything you want to stay put. Make waves with our ROC SAC Ballast Bags! Whether you're looking to boost your surf wave, anchor your jet ski, or just weigh something down to make it stay put, these self-fill bags are the perfect solution for all your ballast needs. New for 2023, ROC SAC Ballast Bags now have a longer roll top for a completely secure and leak free seal. Made from ultra durable, waterproof materials, ROC SAC Ballast Bags can handle whatever you ask of them. They are also great for tent weights, ballast for balancing small watercraft, weighing down photography equipment and much more!