So stretchable you will not believe how much you can carry! This handy pack can fit a water bottle or large mobile phone. The interior has a water-resistant lining to protect your valuables from sweat. And the flush-shut zipper feels smooth, stays shut tight, and provides a reflective surface to on-coming lights. The elastic belt has a sturdy snap closure; the FITZIP adjusts from about 27 to 40 inches.