This bag is specially made for our ZEGA cases. It fits perfectly inside the case so you can make full use of the packing volume. And to help you pack as much as possible in the smallest possible space, the inner bag has a valve so the air can be pressed out when rolled up. You can make use of every cubic inch of the pannier and don't end up packing air. Made of a robust material with Ortliebs popular roll-up closure.