The bag attaches to the underside of your bike saddle/seat with three velcro straps holding your seat & seat post. An aerodynamic rounded shape minimizes wind resistance when riding, and water resistant material and a water proofed zipper prevents your valuables from getting soaked in the rain. It is made of a soft, reflective and translucent plastic reinforced with a fine layer of netting. Simply drop a light in it, and you have yourself a “FIREFLY” lamp!