This is what I would call an "unconstructed" bag since it has no padding or thick materials to give it structure.

That's actually a plus, if you like to move fast and light. Black Diamond designed it for lugging rope and gear to a climb, not for hauling up with you.

This is essentially a duffel with backpack straps, and that makes it work very good for soft goods (like gym gear - judo or jiu jitsu) or for travel.

Since it doesn't have compartments to help me organize, I use mine in travel as a checked piece to hold my jiu jitsu gear and any extra clothing I might want. (My emergency clothing and toiletries, netbook, knickknacks go in my carry-on bag.)

It's easy to throw this simple duffel into the trunk of a taxi where I arrive, and if I have to carry it myself I use the shoulder straps. Since there is no padding on this bag, you leave fragile stuff out of it or wrap in in clothing.

At first I wondered why the backpack straps don't have a stow-away slot like on a convertible travel backpack. But then I realized that would add weight, bulk, and expense (a convertible travel backpack costs a lot more). Now I like the design just the way it is.

And oh yeah if you leave the rope tarp at home, you can flatten this duffel down to nothing and stow it in another bag to use for over-flow (souvenirs etc.) when you come home.

BTW sometimesI use the rope tarp as a clean place to stand if I am changing into my jiu jitsu uniform on a dirty floor.

This pack is best suited to lightweight hiking where you don't need a bear canister and don't need to carry more than 2-4 quarts of water (water is heavy).

My Jam has been ideal for trekking between the tent cabins on the High Sierra Camp loop at Yosemite.

It's not so big it's clumsy, hot, or heavy, but I can still carry a warm synthetic fill sleeping quilt so I don't have to use the fairly nasty blankets provided by the camps, and there is also enough room room for a puff jacket or thermal fleece for cold evenings and mornings at camp.

Best of all, since I don't need some of the stuff that regular hiker needs (like tent or tarp, cooking gear, food) I don't have to "stuff" my quilt or jacket which extends their life.

I also like being able to use either a hydration bladder with tube, or external water bottle.

The outside pouch provides some basic organizing, but this isn't a pack with a million secret pockets. The main compartment, two side slash pockets, and front pocket are plenty, though.

I consider my self a lightweight hiker, and this bag is more than ample for my summer hikes with "comfort" clothing (I like to stay toasty), snacks, and emergency overnight gear. But this pack is also a favorite of ultralight hikers with 1 pound bags, alcohol stoves, and other stripped down, streamlined gear.

It kills me when I see hikers on the High Sierra Camp circuit weight themselves down with much heavier packs for the light duty hiking required for the High Sierra Camp circuit. On the other hand I'm flabbergasted by those who just carry a daypack and look miserably cold because they didn't bring a really warm sleeping bag or really warm jackets, etc. The Jam strikes the happy middle ground, bigger than an oversized daypack, much lighter than most backpacks you see on the trails.

This review is based on ownership and extensive use of the first generation Jam, and inspection of the second generation model (the Jam2 offered here). I will purchase the Jam2 in summer of 2009 since I like the improved shoulder straps with Brock foam much more than the first generation straps (no padding to speak of).

Also the compression straps on the new model add a lot more versatility - without compression straps (lacking on the old model) I pretty much need to fill the pack or my gear will sag or shift around.

Generally, though, the Jam2 is an evolutionary and not revolutionary upgrade over the original Jam.

Isn't that everyone's real question - why is it priced so high? Well, because it uses the best available materials - it has high water repellency and dries fast if the rain was really hard and long, it's impeccably made, and, yes, it DOES breathe unlike its many, many cheaper competitors. And I'm not talking about sleezy knockoffs, I mean it is much better than anything to date from the other Big Name outdoor companies.

This and some silkweight or lightweight base layer will get you through most of the summer in most parts of the Sierras (well plus something warm for nighttime, either an R2 or something light and puffy).

The original Windshirt from Marmot had shirt style tails - split at the sides; no pockets; a slightly lighter lining; and a slightly lighter shell fabric. In short, it could be worn without base layer, as a classic windshirt in cold weather; it could be worn over a base layer as a midlayer; or it could be worn as a sort of jacket over a heavier base layer. But those shirt style tails and the light glossy shell fabric made it look out of place in a cafe. And the lack of pockets, either for junk or for handwarming, also placed it a notch below a true jacket (on the other hand, as a windshirt weighing only 10 ounces it was superb).

Time passes. The current generation Windshirt is still light and useful on hikes, but can also double for light city wear. It is still thin, too thin for standing at a snowy bus stop, but it is just right for an urban hike in cool to downright cold weather (your hiking keeps you warm).

It has a straight hem now, like a jacket; pockets; a slightly thicker lining; and a slightly more substantial shell fabric with a nice "hand".

It's STILL much lighter and easier to stuff in a carryon travel bag than a Land's End Squall (which has a heavy supplex shell, heavy Polartec 200 lining). I find myself using this current generation Marmot Driclime Windshirt as a lightweight casual jacket, especially for travel, but it's still technical enough for hiking (mesh instead of shell at the armpits and other touches like that) on real trails or doing serious city walking. It's grown a little heavier, about 4 or 5 ounces more, but it's still lighter than its competition.

Marmot continues to innovate. The new generation isn't so much a replacement as a rethinking. Enjoy!