Other features include compression straps, moisture management polyester mesh, and hydration system capability with a hydration tube exit port and internal compartment. Water resistant and durable, it's made of a 210D oxford weave nylon with polyurethane coating. The hip belt accommodates waist sizes 24 to 52 inches.

Amazon.com Backpack Guide
Finding the Right Backpack
For extended trips into the backcountry, there's no getting around the fact that you'll have to carry life-sustaining supplies on your back. Here are some things to keep in mind when shopping for a backpack:

Internal vs. External
Up until late 1970's, external frame packs--which consist of an exposed, lightweight metal frame attached to a fabric pack-bag--were the only thing going. In recent years, though, packs that place the support structure of the pack inside the pack, known as internal frame packs, have boomed in popularity.

The good news about internal frame packs is that they hold the weight of your load close to your body, making it easier to maintain your balance on uneven terrain. Meanwhile, internals provide stiffness and support, but they are not completely rigid, which makes them more flexible when you're doing active sports. With the added flexibility comes a high degree of compressibility, meaning you can use the pack's compression straps to cinch down your load and keep items from shifting and throwing you off balance. Internals also sport slimmer shapes that allow for more arm movement in all directions--another big plus for off-trail bushwhackers, skiers and climbers. Last but not least, internal frame packs offer a greater range of adjustability in the shoulder harness and hip-belt than external frame packs.

There are some negatives for internals. First, once packed, it can be difficult to grab needed items out of them quickly. And because internal frame packs consolidate the load into a single, body-hugging unit, proper packing is very important. To distribute the weight properly, you should pack your heaviest items close to your back and in the middle portion of the pack-bag. Plan on getting a sweaty back with an internal, too, given the fact that they are pressed right against you. Finally, internal frame packs are priced higher than external models.

External frame packs are very good at focusing the weight of a load directly to the right place: your load-loving hips. While internals, when properly packed, do this effectively, too, you can always rest assured that an external will distribute the load evenly, no matter how unevenly packed it may be. Externals also offer easy access to your gear via multiple, easily-accessible compartments. Plus, because externals don't situate the load directly against your back, you'll enjoy far more air flow. Finally, if you're on a budget, or you're buying for a growing child, externals are more affordable.

If you plan on hiking on easy to moderate trails and you don't need a lot of body movement, you'll probably be fine with an external. But because externals are so rigid and inflexible, challenging trails or any kind of off-trail pursuit can become painful and frustrating. Also know that your balance is far more compromised with an external frame pack during activities like stream crossings and hops through talus fields.

Packs for Shorter Trips
In addition to backpacks designed for overnight trips, rucksacks are great for day-trips, warm-weather one-nighters, single-day ski trips, or fast alpine assaults. Some rucksacks blur the line between backpack and rucksack with integrated internal supports and sophisticated hip belts and shoulder harnesses. Choose a pack in this category based on your intended use. Short day hikers don't need an internal frame, while climbers and skiers with heavier loads likely do.

Sizes and Capacities
Packs in the 3,000 cubic inches and lower category are good for day hikes or overnighters in warm weather with minimal gear. Packs in the 3,000 to 4,000 cubic inch range are good for one- or two-night trips in colder weather. If you're going to be out for up to three days, look for a pack in the sub-4,000 cubic inch range. Choose a pack with 5,000-6,000 cubic inches for week-long outings. And finally, for trips lasting a week or more, you'll need something in the 6,000-plus cubic inch category. Keep in mind, though, that bigger packs weigh more, and since every ounce counts, you'll want to choose a pack that offers just enough space for your outings and no more.