Picture, if you will, a really crummy backpack— say, a burlap bag chock full of russet potatoes with a pair of hemp-twine shoulder straps sewn on. Sure, it'll carry your load. But spud-induced gravity will wreak agony on your shoulders. The straps will gouge your epidermis. And the load will sway with every stride until it becomes an obnoxious tail wagging you, the masochistic dog.

Big trips call for a big pack, like the
5,340-cubic inch Dana Designs
Terraplane.

With this image in mind, it's easy to appreciate the design elements that make a modern internal-frame backpack an impressive conveyor of payload. Through the evolution of trial and error, the shoulder-slung sack has given way to a complex composite of foam, aluminum and plastics conceived to minimize the effort of hauling potatoes and other essentials. These contemporary packs came in all shapes and sizes, from ungainly expedition models to slimmed-down day versions, but the elements that distinguish the better ones are consistent across the board. So what makes the apotheosis of the breed so great? Peel back some Cordura and take a look inside.

Robert Earle Howells has been a correspondent for Outside Magazine for 11 years and is the editor of Outside's annual Buyer's Guide. He started backpacking in the Sierra 25 years ago, and still frequents the Sierra as well as his local San Gabriel Mountains. Bob taught mountaineering classes for the Sierra Club in the early '80s, which is when he was turned onto gear geekdom.