The Ortlieb Back Roller is an easy to use pannier for your bike's rack. The material is 100% waterproof and all seams are sealed for complete water protection. The bag can be mounted on either side, and if you so wish you can buy another one later on. This model boasts the QL3.1 mounting system. Just install the included mount set on your rack, and enjoy super easy day to day use. One of the extra images displays the mount and a rear rack. Rear rack not included. - Free model: does not contain PVC - Roll-up closure - Shoulder strap - Flat inner pocket with zipper - Reflectors - Welded seams - Five year guarantee Volume: 20 liters, if the mouth of the pannier is rolled enough to keep them waterproof. You can gain extra space at the cost of water protection by rolling the top fewer times.