Pack Type

Decades ago, external-frame packs were standard. The design, with the visible aluminum bars that support the load, works adequately, so if you inherit a hand-me-down or find a cheap model, don’t be put off by the awkward-looking construction. But almost all modern packs are internal-frames (pictured), which means that the frame—the part of the pack that supports the load and helps keep its shape—is integrated into the body of the pack. The result is more comfortable and compact and balanced than external frames.

Size and Capacity

The size of your backpack refers to a brand-a...