I can't imagine a hip pack with a 70 or 100 oz capacity. It seems it would be pretty cumbersome. I received my hydration vest yesterday and I've only tried it on so far. It fits like, well, a vest. I'm anxious to fill up 50 oz bladder to see how it feels. It actually has several storage compartments so I think it will definitely be my go-to hydration pack for the summer.