While both cargo bags and cargo boxes offer top-carrying solutions, they differ considerably in terms of their advantages and disadvantages.Cargo bags: If price is a primary issue, this is your best choice. Car top cargo bags can be much less expensive than comparably sized boxes. They are lighter and more flexible, and they are often easier to store because you can fold them. Some cargo bags can be used with a car rack.Cargo boxes: Usually constructed with a hard shell, cargo boxes provide much more protection than cargo bags. They are generally sturdier on the road, and the majority feature locking options, something rarely found in cargo bags. Cargo boxes tend to cost more than cargo bags, and a roof rack is required to securely mount the box to your roof.