Selecting a pack can be confusing. It's a good idea to rent or borrow one or two types before buying if possible. A correct fit is as important as overall capacity (volume) and packing technique. Outdoor equipment dealers are usually available to help explain the fine points of each of these topics, but we can review the basics here.
Internal vs External Frame
There are two types of packs used by modern backpackers, external and internal frame. The external frames are the kind which have metal or heavy plastic poles which you can see. The cloth bag part of the pack is then attached to this frame. For the internals, the frame usually consists of metal rods or even stiff synthetic slats, called stays. These are located in special pockets that are located on the part of the pack next to you back. So on internal frames you don't see any poles at all, all the metal poles or synthetic slats are sewn into the pack.
So, which is better? Naturally there are trade offs (though judging by the available selection the market place is saying that internal frames are the design of choice). External frames are noted to be easier to actually pack your equipment in because they have more pockets and because it is easier to tie things on the outside of the pack. An internal frame pack is known to be more comfortable than an external frame, especially when backed and fitted correctly! Where the external frame usually only touches your back in a few places, the internal frame is made to fit straight on your back, more evenly distributing the weight.
Pack Capacity (volume)
Capacity (volume) is the next big issue. The capacity of the pack you need depends on what you will be doing. Pack capacity is usually quoted in cubic inches (c.i.) and liters (l). Capacities usually range from 3,000 to 7,000 cubic inches. Large day packs are usually around 3,000. These might be used for overnight camping if you don't plan on taking much. A good weekend or long weekend (3-5 days) pack ranges around the 4-5,000 c.i. range. If you really wanted to you could take one of these packs on a longer trip, but it would be a tight fit. If you are going out for a long time, over a week with lots of equipment, you might think about a pack around 6,000 c.i. That will give you plenty of room to pack what you need and not worry about space. Any pack over 7,000 c.i. is generally made for long, winter expeditions, or people who feel like they should take everything the own with them on their trip. Starting with an entry level pack in the 4-5,000 c.i. range is a good approach.
Pack Fit
All packs come in different lengths intended to match the users torso height. Torso height is measured from the belt line to the top of the shoulders. Packs for taller users are intended for 18 inch and longer torso lengths. Packs for medium height users are typically adjustable for 17 to 20 inch torso lengths. Each brand varies, so it's best to try the pack on and be sure it can be adjusted to fit correctly. As a first step, measure your torso length. Select a pack that is intended for your torso length. With the shoulder straps loosened set the pack's waist belt so it centers on your belt line {fig. 1}.
Tighten the waist belt so that it firmly encases the hips.
Gently tighten the shoulder straps and the hip belt stabilizers {fig. 2}.
Next, adjust the top stabilizer straps and make final adjustments to the shoulder straps until the pack feels comfortable {fig. 3}. Note that the stabilizer straps can be adjusted on the move to allow for the angle of the terrain; tighten more for downhill; loosen for uphill. The shoulder straps should be shaped to curve round the shoulders reducing stress in the neck and shoulder muscles.
Finally, adjust the chest strap (sternum strap) for the best fit {fig. 4}.
When adjusted to feel comfortable, check the distance from the top stabilizer strap attachment point to the shoulder. You should have 1-1/2 inches of clearance here for a properly fitted pack. If it is less, the pack is intended for torso shorter than yours. If it is more, the pack is intended for a longer torso.
Prices
External frame packs tend to be less expensive than internal frame models with comparable features. Prices vary widely with features, volume, and brand name. Expect to pay in the $100 range for a new entry level internal frame pack in the 4-5,000 c.i. range. This would not be a brand name pack, but would be quite serviceable for most hikers. Spend more only is you're sure this is the sport for you!
Used packs can be considerably cheaper; check eBay, the classifieds and of course with other Scouts in your unit!
This page revised April 20, 2007