A very handy container for your pocket items or a water bladder.At 135 cubic inches, the seat bag is large enough to hold your wallet, keys, bike tools, etc. It will even fit most standard size water bladders. The bag slips over the back or bottom of the seat and can easily be removed and carried by a handle on the top. It has a zipper closure under a protective flap. This bag is very durable, puncture resistant, flexible, and water repellant. It provides excellent use of free space and will not interfere with the commuter bag, head rest, rear rack, trunk pack, or panniers. The seat bag fits on the back of the seat or under the front of the seat. Order two if you need extra cargo space. Compatible with all trikes we currently sell. Not compatible with TerraTrike versions 1.9 and older. And it now comes with a reflective strip for safety! (not pictured)