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.

Backpack Types

External-Frame Pack: 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 backband, and a load-bearing hipbelt. 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 waistbelt. 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.

Internal-Frame Pack: 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 hipbelt. 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 hipbelt 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.

Frameless 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.

Top-Loading and Panel-Loading Design

Top-Loading: To pack a top-loader, you just dump gear down into the opening, cinch the drawstring, buckle down the top flap/pocket, and yank the side compressor straps tight. This most popular of bag designs offers high cargo security at some cost in access convenience. Most top-loading externals have a metal spreader bar that holds the main compartment open, so you can simply lean the frame against a tree and shoot baskets until it's full. Most internal-frame top-loaders also sport a sleeve-and-drawstring system that helps compress the cargo. Access to packed equipment in a top-loader isn't bad if you keep oft-used items near the top, utilize any access zippers, and/or organize gear in color-coded stuffsacks. A top-loader is packed easily while upright, offers fewer openings for rain to penetrate, and has fewer zippers to blow out.

Panel-Loading: The main cargo compartments of a panel-loader open wide with curved access zippers, This design makes this type easier to pack than a top-loader. Finding the widget of your immediate need may still require a little digging, but you can usually locate it more quickly in a panel-loader. A panel-loader has to be angled or laid down to load, and for durability's sake, the zippers should be heavy-gauge coils backed up with buckled compression straps. But for the most part, a panel-loader is plenty durable, easier to load, and almost as weather-proof as any top-loader, especially since you'd use a raincover with each style. Now that many packmakers have adopted high-volume hybrid top-load/panel-load bag designs, you can have it either way.

Capacity

Capacity ratings are expressed in cubic inches as supplied by the manufacturers. These aren't much more reliable than the notoriously mythical temperature ratings for sleeping bags since no industry standard exists. Capacity ratings offer limited comparisons value between manufacturers but generally hold true for comparing models within each manufacturer's line.

Compounding the problem is the fact that internal and external packs with comparable capacities may have widely differing cubic-inch ratings since sleeping bags end up outside the pack bag on most external-frames but go inside the bag on almost all internals. A reasonable rule of thumb: Sleeping bags run between 800 and 1,500 cubic inches, so subtract that figure from an internal's cargo-capacity rating when trying to compare it with a similarly sized external.

Light Overnight: This pack type takes in mostly slim-profile internal sacks tailored to ambitious day pursuits like rock climbing or ski touring. But this type is also appropriate for one to three nights with honed-down, bare essentials gear. Most packs are frameless rucksack designs; zip/panel loaders are popular in these sizes. Overload these packs when shopping, because that's often how they're carried. Double-check to make sure your sleeping bag fits without hogging all your cargo room. Look for carrying stability. Capacity: 2,500 to 3,500 cubic inches.

Weekend Pack: A weekend pack should be short on frills and long on utility. It'll hold a compact sleeping bag, small tent, stove, a little food, and miscellaneous equipage for the weekend. A smaller sack forces you to travel light because there simply isn't room to bring all your toys. Capacity: internals, 3,000 to 4,500 cubic inches; externals, 3,000-plus cubic inches.

Long Trip: This category includes the basic "load-monster" pack for most multiday hardcore travel. It's big enough for a winter week, yet it's not too big for a summer weekend. Ultralighters could make do for weeks in most climates. For the occasional expedition, add side pockets. Capacity: internals, 4,500 to 6,000 cubic inches; externals, 4,000-plus cubic inches.

Expedition: This pack type can swallow far more gear than you'd probably want to carry, and it can keep it safe from hostile elements. In this size range, fit is absolutely critical. Before you buy, try the pack with 60 pounds aboard because that's the sort of heinous load you'll be carrying. But be warned: With this much cargo space conveniently at hand, there is a tendency- to take things you don't really need. Look for extra-beefy shoulder straps and hipbelt, lots of lash points, expandable top lid, and seriously cavernous compartments. Capacity: internals, 6,000-plus cubic inches; externals, about 5,000-plus cubic inches.

The harness and waistbelt are any backpack's most important features.

External-Frame Pack: How to fit it

Load the pack, ensuring that the hipbelt fits right, then adjust the shoulder straps. Getting those two systems work-

l) The hipbelt should rest on your hip bones. The padded section of ! the belt should wrap around your hips but not quite meet in front. You may have to move the belt up or down on the frame so the pack's lower crossbar doesn't contact your back.

2) The shoulder straps. With most frame packs, the shoulder straps' upper anchor points should be even with the crest of your shoulders. The straps should be set wide enough apart so they don't pinch your neck, but narrow enough so they don't slide off to the side. If the straps are mounted too high, they'll transfer weight to the front of your shoulders and "wedge" you in I place. Set too low, they'll take too much of the load, won't let the waistbelt share the burden, and tend to let  the pack sway.

3) The load-lifters. Shoulder straps equipped with load-lifters generally should join the frame just below your shoulder crest. The load lifters themselves should join the frame at ear level, and attach to the shoulder straps just forward of your collarbone. Tightening the load-lifters transfers more weight onto your shoulders. Loosening them will settle more weight onto your hips. You can vary the load-lifters' tension while you're on the move to help ease the burden when you've packed too much stuff.

4) Frame size. You can tell the frame is too small when you run out of headroom, can't get the shoulder straps and waistbelt far enough apart, or you can't let out the shoulder straps enough It's too big when the top flops around or the shoulder straps bottom out against their adjustment buckles.

External Frame Packs: How to load it

Make these four simple steps a routine when packing:

l) Heaviest gear goes on top. Carry weight too low or too far back and you'll have to lean forward to counterbalance it all, which may turn you into a hunchback before your trip is over. Weighty stuff; stove, cook kit, bulk foods, stormgear, water bottles go in the upper compartment and top side pockets. Keep the heaviest items close to your back. Store fuel bottles and water bottles upright in separate pockets to avoid contaminating food or clothes. The tent, usually the heaviest item carried, is lashed on top behind the extender bar. Odd-shaped cargo fits under the top lid.

2) Midweight gear fills the middle. Stow clothing, personal gear, headlamps, maps, compass, compact camera, and the like into the center compartment and lower side pockets. Stuff spare clothing into a plastic bag for good storm insurance. Organize similar gear in separate pockets.

3) Light, bulky equipment goes toward the back of the pack. Lash your sleeping bag below the main pack bag. Always line its stuff sack with a plastic bag; after hiking all day in the rain, you'll be glad you did. Or carry the sleeping bag in a daypack you can use on side trips.

4) Lash long items to the frame. Tie your flyrod case and long tent poles to the sides of the frame, or shove them into tunnels behind the side pockets. An ice ax will fit into the pack bag's loop carrier.

Internal Frame Pack: How to fit it

Start by stuffing the pack full and ensuring that all straps are loose. From here, it's a matter of putting it on so you can check for a comfortable fit. 

l) Fit the frame. Slip into the shoulder straps and fasten the hipbelt where it's most comfortable, generally centered over your hip bones. Watch your profile in a mirror to see if the framesheet or stays protrude 2 to 4 inches above your shoulders; if less than that, look for a larger size. Longer stays can restrict headroom even though the suspension fits.

2) Fit the waist. The padded ends of the hipbelt shouldn't quite meet in front. Make sure there's enough room to change layers of clothing. If  the unpadded part rubs your tummy, guess what? Gotta find a bigger hipbelt. Overtightening the hip stabilizer straps can distort the belt shape and fit.

3) Fit the shoulder. Shoulder straps should curve over your back and join the pack roughly 2 inches below your shoulder crests. Reposition the shoulder harness if necessary. Cinch shoulder straps so the lower ends are about a hand's width below your armpit. If they bottom out or come up short, find a different size pack or parts.

4) Fiddle with the load-lifters. These divert pressure to the front of your shoulders. The upper ends should join the frame at ear level. If you can't position them above shoulder height, find a larger frame. It's important that the buckle attaching the load-lifter to the shoulder strap be positioned just in front of your collarbone. Tighten the load-lifters to shift weight onto your shoulders, and loosen to shift the load to your waist. Vary them on the trail to give your back a break.

5) Fiddle with the other doo-dad. By now, a bit of fine-tuning should be all you need to achieve the ideal fit. Cinch the various hipbelt and/or pack-bag stabilizers to pull everything snug against your waist, but don t distort the smooth wrap of the belt. A sternum strap should be set a couple of inches below collarbone height. If the frame stays are shaped properly, the pack will comfortably hug your back.

6) Reshaping the frame. Shaping the frame stays remains a black art. Most frames come prebent to comfortably fit the majority of users. If you aren't among that privileged majority, we recommend working with a skilled packfitter, especially if the pack has a framesheet. But the merits of bending your own shouldn't be slighted; just keep a tracing of the original profile.

How to load it

An internal's cargo creates part of its load-bearing structure. Once filled, the pack stands tall, but with contents removed, it becomes a heap. Merely filling the pack, however, isn't enough. You need to think carefully about the order in which your gear nestles into the pack. For level hiking over easy terrain, try to create a high center of gravity. Place loose clothing and other high-bulk/low-weight items low in the gear department, gradually adding heavier, denser items on top (food, stove, water bottles). For more active pursuits like bushwhacking, skiing, or climbing, keep the dense stuff lower and closer to your back to retain a compact center of gravity. Many women, because of their naturally lower center of gravity, prefer the latter packing technique for all occasions

How to put it on

Once loaded, there are several ways to put your pack on without pulling your back out:

l) Set it on a boulder, stump, or downed tree, slide your arms into the straps, then lift with your legs.

2) Bend your knees in a semisquat position, then lift your pack onto one of your thighs. Slide your right arm into

the right strap. With the strap and the pack's weight on your right shoulder, swing the pack around and onto your back while sliding your left arm into the left strap.

WEAR IT WELL : Advice on loading, fitting and using packs