A modern pack can seem to defy the laws of gravity, making 60 pounds carry like 40, and making 30 pounds feel like a heavy shirt (almost). If you're carrying an older pack, you may find yourself stripping it off regularly to relieve shoulder spasms and tingling fingers. Conversely, a good, correctly fitted modern pack will rarely leave your back sore (same weight, more comfort). And the heavier your payload, the more critical the pack quality becomes.
Virtually all packs are made of nylon, foam and aluminum and fall into three basic categories: external-frame, internal-frame, and frameless rucksacks. External-frame and internal-frame packs are the most appropriate choices for multi-day trips, while frame-less packs are best for light, fast ovenights or big day loads. Choose your pack based on the type of trips you will be taking.
The external is the venerable purist's "back- packing" model, made with an H- shaped exposed frame suspended by thickly padded shoulder straps, a stretched back band, and a load-bearing hip belt. Straps or wired clevis pins attach the pack bag to the frame. An external carries best with the weight high over the shoulders, supported largely by the waist belt. It offers good ventilation against your back, a relatively straight-up stance, and heavy load-hauling capacity. However, the same high center of gravity also makes the external shaky in the balance department, often causing the wearer to sway during active sports like skiing, bushwhacking, and boulder hopping. A typical external pack bag bristles with side pockets and compartments, allowing for easy gear organization during long trips. Externals come in simple top-loading and easy-access panel-loading versions or combinations. Look for strong bag-frame attachments and a comfortable initial fit with good weight transfer to the hips. After that, check for adequate shoulder-strap padding and thoughtful pocket configurations. Strap on the pack, snug it tight, then look up. Your head will probably hit the frame, so find one with reasonable clearance. Although externals remain popular, they've lost ground to the recent wave of Internal-frame models. An external is typically half the cost of a comparable Internal.
An internal incorporates the load-transfer elements into the pack bag itself, using flexible stays of aluminum or graphite to transmit weight onto a padded, stiffened hip belt. A flexible plastic frame-sheet adds support and guards the spine from protruding cargo, yet has enough "give" to match your moves. An internal hugs tighter to the body than an external frame and carries the load somewhat lower so it's more stable for climbing or rock hopping. The streamlined shape offers better arm clearance for awkward maneuvers, and slips through tight spots where you'd be dragging a bulky external pack behind you. Many people buy internals because of their "mountain jock" image, but these packs do have their drawbacks. You lean forward more under an internal than with most externals. Proper loading is critical because the cargo itself helps stabilize the whole structure. Side pockets usually have to be purchased separately. And most significant, a better internal pack can cost $350 and up, though even the fanciest external rarely tops the $200 mark. Look for a good harness fit, where the hip belt centers over your hip bones and the upper ends of the shoulder straps attach to the frame 2 or 3 inches below shoulder level. The tops of the frame stays should protrude at least a couple of inches above shoulder height, but no more than 5 or 6 inches.
Match the pack-bag size to your intended uses. Simple, flat-bottomed sacks stand up better for loading than those with tapered sleeping-bag compartments. Since all your stuff should fit inside an Internal, take key items such as tents and sleeping bags along when you're shopping.
Frame less Rucksack:
A rucksack in the midsized range (2,500- to 3,500-cubic-inch capacity) actually sports some sort of frame. A simpler incarnation is just a well-tailored bag with a foam-padded back panel and shoulder straps atop a webbing waistbelt. The smaller end of the rucksack range is best suited to light-load activities such as hut-to-hut hiking, grocery shopping, backcountry skiing, rock climbing, and day-tripping, anything where the freedom of motion is ample reward for the smallish capacity.
Suspension varies widely in this category. The better sacks incorporate flexible plastic framesheets, shoulder-strap stabilizers, and stiffened padded waistbelts. These models can usually handle 30 to 40 pounds; heavier loads depend on your grit factor. A frameless rucksack requires careful packing to carry well, since the stuffed pack bag s your load stability.