DIAL IN YOUR WAVE - Easily move ballast from side to side or back to front to fine tune your wave. No more shuffling friends and family around your boat. PREFILLED and LEAK PROOF - Comes loaded with a sand/gravel mix for a weight of 45 lbs per bag. Tall roll top with secure hook and loop closure seals contents inside the bag to keep your boat (or anywhere you use the bag) clean. 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 15" x 12" x 5.5". 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 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 prefilled, 45 lb 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. ROC SAC can be easily emptied and refilled with the fill material of your choosing (rocks, gravel, sand, steel pellets, tire weights, etc.). 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!