Daypacks
Daypacks are generally designed for short day trips, though with judicious packing, they can sometimes be used for overnight trips of a day or two. These packs can generally hold up to 3,000 cubic inches, though most are designed between 2,000 and 2,500 cubic inches. Some also have features that climbers would enjoy, such as an ice axe loop on the back. The Osprey Stratos 40 is a great pack in this class, weighing only 3 pounds 4 ounces. Those seeking a little more functionality should consider the Arc'teryx Khazri 55, which can be stripped down by removing the aluminum stays to save weight.
Expeditions
Those going on expeditions, or doing through-hikes of the Appalachian Trail, need a pack with a little more carrying capacity, between 4,000 and 6,000 cubic inches. The Arc'teryx Naos 55, which, with extension collar can just hold 4,000 cubic inches, is a great choice, especially because of its water resistant fabric construction. Those needing more carrying capacity should look at the Gregory Whitney 95 Backpack, which is available in three sizes between 5,300 and 6,300 cubic inches. The Osprey Aether 70 is another good option, carrying well and being relatively lightweight.
Women's Specific
While men's backpacks can work for women, many women hikers will find women's specific packs, which have a narrower shoulder strap configuration, wider hipbelt, and shorter torso design, to carry much more comfortably. Many different companies make women's specific packs. For weekend and day trips, the Gregory Jade 50 and Osprey Aura 35 are good choices. For extended trips, the Arcteryx Briza 62, which even has a pocket for a Camelback hydration bladder, is an excellent choice. The Gregory Deva 70 is available in three sizes, from XS to Medium, and the Osprey Ariel 75, holding 4,600 cubic inches, is good for many multi-day trips, but not for really long ones.
