Ladies backpacks are fundamentally different from backpacks designed for men. Because women generally have a shorter back length in comparison to their height, wider hips, and shoulders that are less broad than men's, it makes sense to build packs differently for the female form. Most of the larger packs have adjustable carry systems and straps but they are built to fit women's bodies best. It's not just a matter of style and color, although we believe there is no reason that outdoor gear can't have style too.
Day packs for women need to be just as big as the men's version. Between 25L and 35L is the ideal size. If you expect to be carrying a heavy load or hiking long distances with the pack on your back, look for a contoured waist belt to avoid putting too much pressure on the points of your hip bones. Some models come with integrated rain covers, which saves you buying a separate one and means that it's always there if the weather changes unexpectedly, and many have space for a hydration system too. A few of the larger packs even have a detachable top section that can be used as a lumbar bag in its own right.