Ultimate Direction says 

This lightweight, women's-specific fit FastpackHer allows you to move fast in the backcountry with a durable design that checks all the feature boxes. True to our roots, it uniquely fits like a vest with water bottles up front, but distributes weight like a pack. We gave it an upgrade with Infiknit? and FastFlow technology to increase the backpanel's breathability and moisture wicking. This do-it-all pack also has plenty of dedicated external storage, a roll-top opening and a full-side external zipper for easy access to anything inside.