External Frame Backpacks
Also used for big, heavy loads, these packs are best for walking on trails (as opposed to skiing, climbing or bushwhacking). That's because the packbag is hung off a simple exterior frame, so the load is positioned farther away from your back. And though this might result in a wobble-fest for climbers or skiers, trail walkers who carry big loads often love them. (Tip: Use hiking poles for stability.)
External frame packs have a higher center of gravity than internal frame packs, which has two advantages: It gives excellent weight transfer to the hips and it allows you to walk with a more upright posture (with big internals you have to lean forward to counterbalance the load). Plus, they offer lots of airflow between the pack and your back, great for long, sweaty days on the Appalachian Trail or anywhere that heat is a factor.
Externals are known for their plentiful pockets and ultimate trail-livability, but there are still a few tricks to loading them.
Backpacker Tip: Loading an External Frame Backpack
Most externals assume that you'll strap your sleeping bag outside and under the packbag. That's why it's absolutely critical that you store your bag in a completely waterproof stuffsack. (Tip: External frame-pack wearers are rolling the dice if they rely on garbage bags for water protection. Walk too close to a branch and you're sleeping on a sponge. Spend a few extra bucks and get a waterproof sack with a roll-top closure.)
Heavier gear (like your food and tent) belong higher up on the frame, but still close to your spine.
Use any available side or front pockets to organize your gear. This allows you to skip the stuffsacks and save a few ounces.