This is intended for larger rucksacks (50+litres) which will be used for backpacking - it is important you get the right rucksack for you! Smaller rucksacks (20-45 litres) do not matter so much as the load in the bag is a lot lighter and less crucial while walking. Some of the below advice still applies for smaller packs though.
What to Look For (Internal Frame):
1. Double bottom with differentially cut inside layer - puts weight on inside layer, significantly prolongs life of pack.
2. Slim profile, especially if travelling off-trail.
3. Straps (removable) and loops for transporting sleeping pads, ice tools, etc.
4. Compression straps to enable a slim profile and stable load and for carrying poles, wands, etc.
5. Load-lifter straps to pull the load off the top of your shoulders.
6. A belt that cups over your hip bones, so the pack's weight is evenly distributed over the entire belt surface and not just on the part of the belt that rests on your hip bone.
7. Preferably, double zippers--in case one blows out, you won't lose functionality.
8. Head clearance. You might want to look up (without hitting your head) to see where you are going.
Fitting a Pack:
First, a brief word about fitting a pack. As with boots, proper fit is the key with a backpack. The weight of a pack is secondary, since a well-designed, heavier backpack may give you a more comfortable ride than a much lighter pack carrying the same load.
NOTE: Although weight may be secondary, it is nonetheless very important. For example, don't automatically settle for a large (50+Litres) pack when you mostly carry 30-40 litres. Firstly, understand your needs and how you're going to use this thing. There are an increasing number of lightweight packs coming to the marketplace which might serve you better.
Know your torso length.
Lack of this knowledge often causes an uncomfortable realization, after the fact, that the pack doesn't fit correctly. The reason you must measure your torso, rather than guess what size pack you should have, based on your ability or size, can be illustrated as follows: a large, tall person can have a short torso (and long legs) thus requiring a smaller pack. A shorter, smaller person can have a longer torso (and shorter legs-like me) and require a larger pack. All pack makers design their packs with your torso in mind. Thus, measure your torso, preferably before shopping, so you will have that knowledge in your pocket. This will, hopefully, eliminate total dependence on outdoor-shop salespeople, who sometimes make mistakes !
To determine your torso size, ask a friend or family member to help you, if possible. You will need a tape measure or tailor's tape to measure along your back from the seventh vertabrae--the largest bump on the back of your neck, with your head forward--to a point on your lower back which is hortozontal with the top of your hipbones. If you find that your torso is on the border between two sizes, my experience is to go with the larger size. For example, if your torso is 18 and a small size is torso 16-18, and a medium size is 18-20, go with the medium because you'll have more room to make adjustments. Most good packs allow for that.
The rest of the fitting you will need to do, although important, has more to do with what feels good. It seems like I'm always getting a hipbelt or shoulder harness that feels right to me but doesn't match with the manufacturer's fitting instructions. But a couple of things you should look for:
The hipbelt should wrap around your hips, not your waist (or stomach) and the lumbar pad should be centered properly into your lumbar area. You want a significant amount of the pack's weight on your hips (and, if you're like me, on the lumbar region). A good way to do that is to make sure your hipbone is centered under your belt (and the lumbar pad centered and pressing firmly into you lower back).
Get a shoulder harness that doesn't get in the way when you swing your arms or have buckles that pinch your skin.
The key for any pack is to try it out with plenty of weight in it. All outdoor shops should have weights and stuffing for testing packs. Fill up the pack with weight approximate to that you would be carrying on the trail. Try to distribute the weight in the pack as best you can. After you have achieved a good fit (and, hopefully, the salesperson concurs) take the pack for a test drive, as follows: Bend over and touch your toes; Sway, dramatically, from side to side; Jump up and down. Throughout these manuevers, the pack should stick to you like glue. It should not feel sloppy, nor, if it's properly packed, should it throw you off balance. Walk around the store many times. Walk up and down stairs. Walk out in the parking lot, through the nearby park, or wherever--assuming it's okay with the salesperson. Take the pack off, loosen all the straps, put the pack back on, tighten all the straps, and walk around some more.
Concentrate on ensuring yourself that the weight is being distributed evenly. You shouldn't feel excess weight in any one spot, unless of course you want it that way. A good pack will provide flexibility to shift the weight around via adjustments. Fiddle around with the adjustments. Shift weight to your shoulders, then to your hips. Each should feel comfortable, because on the trail you will use different adjustments going uphill than you will downhill. Also, when your shoulders get tired on a long haul, you may want to shift more weight to your lower back and hips. Experiment!
Once you've decided on purchasing a pack, ask if you can return the pack, if upon further testing and experimenting at home with your own gear loaded in it, you decide it's not the right pack, after all. Note. Marmot allow you to purchase it, then take it home and try it out with your gear or whatever--keeping it clean, of course--so you can have time to decide if it really is the pack for you. If the pack has inter-changeable parts, Marmot will allow you to bring back parts for exchange--if you don't like the way the hipbelt is wrapping around you, take it back and exchange it. Look for that kind of professional support because it makes finding the right gear a whole lot easier.
Unless you have a bomb-proof, leak-proof pack, organize gear in waterproof stuff sacks or heavy duty zip-loc freezer bags. Color-coded stuff sacks make it easy to locate gear items and is an especially useful way of keeping track of smaller items. Another option is to put a large heavy-duty garbage sack into your pack bag as a liner to ensure everything is protected (this is probably the lightest approach for keeping gear dry but doesn't provide for good gear organization).
Pack a tent on top where you can get to it fast in a sudden storm without pulling out any of the rest of your gear. Also, pack items such as raingear, water, snacks, sunscreen/sunglasses, camera, and other quick access gear items, in an easily accessible location - e.g. right next to side zips, in the pack lid pocket, a side pocket, or on top of the pack, along with the tent.
If your pack doesn't have a framesheet between you and your gear, make sure you pack sharp and hard objects away from your back, preferably toward the outside of the pack, e.g. items like stove, cook pots, water & fuel bottles, and tent poles & pegs.
If your pack doesn't have a bottom compartment for your sleeping bag, and if you are on the trail for extended periods, you might want to consider putting your sleeping bag up toward the top of your pack. Putting your bag at the bottom with all the rest of your gear on top of it won't help the bags lofting ability.
Keep fuel containers away from food and cooking gear. Place fuel containers in heavy duty gallon bags and pack upright.
Strive for a horizontal distribution of weight, so that one side of the pack isn't heavier than the other. You should keep the weight centered so that you don't lose your balance or hurt your back.
Slimmer is better. Make sure the compression straps are tight after packing to help ensure a slim pack profile. Remember, the fatter your pack becomes, the farther you must lean forward to bring the pack's center of gravity back over your hips - fat packs can result in sore backs !
If mainly on the trail, especially for long distance treks, pack the heavier items in the upper portion of the pack, in order to create a higher center of gravity. This centers the pack weight above your body where it's easier to carry (on easy to moderate tread).
If going off trail, pack heavier items close to the back in the middle portion of the pack. This will result in better stability when boulder hopping, post-holing, or whatever.
TWMC c/o John Payne
Tsukuba Walking & Mountaineering Club