This is a large, soft tail-bag with a firm molded base. The main compartment has an inner waterproof liner. I am not sure of the precise volume, but it holds a lot. It is BMW branded, but I purchased it for use on a Suzuki V-Strom and it fit very well. I placed it over the back of the seat, but it is also designed for use over a luggage rack. There are many straps and lots of options for tie-down. There is a shoulder strap as well. The bag is in mint condition - as new. I am the only owner, and I purchased it for approximately $250 from the predecessor of Island BMW.