I have tried alot of packs over the years. Everything from Kelty at the begining, then moving on to Osprey and Gregory Packs, but this Arcteryx Naos is by far the best. First off the main compartment is totaly waterproof if you leave the port for the hydration tube closed, but if you leave the lid on and as long as you don't submerge the pack totaly under water it will keep everything absolutely dry. The zippered pockets are not totaly water tight, but as I said above it will handle everything but a total submerging in water. So leave that pack cover at home, and pray for rain. Another great thing is this pack won't absorb water into its fabric... thus it doesn't get heavier if it gets wet. This is the most comfertable pack I have ever worn. The key difference is the swivel waist belt. It makes for all the difference. The pack is free to move from side to side, but still be anchored to your waist. The material of this pack is super strong... and while I can't attest to it now, this pack seems like it will last a life time. The design is everything you need, and nothing you don't. Two lid pockets (one large, one small), two front zippered pockets (one large, one small), and the cavernous roll top main compartment. I pack light, and tend to be somewhat of a minimalist... that being said this pack is large enough for me to pack enough gear and food for a week long summer backpack, or a 3-4 night winter trip. I plan to carry this pack exclusively.

My first and only time out with this pack so far has been on a trip through the Needles, and surrounding Canyon lands National Park, in Southern Utah.
Water wasn't an issue except having enough of it with you, as none is available there currently. So the only testament to the water proof that I have is the bathtub and the hose which I feel to be every bit as good as real world short of crossing a river with it. Even loaded it wasn't an issue to keep the weatherproof pockets out of the water and the rest in. It's a very great design and works very well.
Loading is easy and there are enough external pockets for quick access. It did get to be a bit of a pain opening the drybag top to switch layers. The front pocket could hold some light layers but not rain gear. A small price for ensuring that your important gear is dry though.
It held up very well. Through the narrows and shrubs I found myself cringing as my pack scraped or as I was stabbed by a tough branch. I was pleasantly surprised at the durability of the pack though as there were no rips, holes, or even visible abrasions to the material. I wasn't sure either with the zippers as I forced the seams shut over my gear in the pockets but they too seemed to cause no abnormal side effects.
As far as the comfort factor goes it distributed the weight very well. All of the straps are comfortable and very adjustable. The disc system made for very smooth movements whether it was a looser fit or strapped tight to your body for more challenging navigation. The pack was just not a burden/limit short of the extra weight.
Also, they recommend the bigger pack for week long trips. I had everything that I could have imagined wanting/needing and it would have been sufficient for a week long trek. ESPECIALLY not having to pack in 6 liters of water I could imagine room for even more and less weight.
My only complaint or biggest that I can think of is poor hydration compatibility, as with most all packs that I've came across.

hey. just took this pack sans lid for a day hike to see how it would do. held up nicely just as it did on the overnighter i took it on a few weeks before.

as a point of curiosity, today at the waterfall/swimming hole, i threw the pack in the water and used it as a flotation device. overall a success, but beware of the outer zippered pockets.. i failed to remember the drainage hole at the bottom of the large one and how the small one is only kept separate by some stretchy, non-water resistant material. i'd imagine the lid isnt dunkable either, but that's for me to find out later.

as a response to the guy who said it was an odd shape at the bottom: i just pack in my sleeping bag without the stuff sack. it fills in the space nicely and you can just cram stuff on top of it. its worry-free, even with my down bag since.. well.. its a drysack.

my straps squeak too.. not sure what to do about that. great pack though. cant wait to use it again.

There is probably a different "best" pack for every person depending on your build, etc., but for me (6ft, thin build) this the best pack I have ever used. The suspension features a flat back, but great padding on the straps and belt. When cinched down, the pack stays slim and in place. The swivel on the hip belt is a nice touch, especially if you are moving around a lot. The material is tough and took a week of rock scraping in Utah with no problems. I love the rolldown top and the fact that this bag can become a dry sack. There's a good pocket for your bladder (something the Needle lacked). Only one complaint, and maybe someone has an idea to solve it: the plastic buckles on the top shoulder straps -- when fully tightened -- squeaked during my hike. Slightly annoying. I loosened them and the squeaking stopped, but would prefer to have them tight and not squeak.

I should qualify this review by disclosing that this isn't the pack for me and I haven't used it on any serious hikes. That said, this is an awesome pack. It's basically a dry-bag with straps, but what straps they are! The suspension features this cool rotating thing that makes it very comfortable to wear (the Needle has something similar).
Quibbles: The bottom of the pack is small and oddly-shaped. My sleeping bag doesn't fit nicely, and I had to put other things below it to fill it out. Because it's basically a dry-bag, it doesn't have any give, and it's hard to slide things around inside. I had a very hard time getting my bear canister packed.
Overall, great pack. Not right for me. Also, really expensive, but if you're seriously considering it, that's probably not the deciding factor.

I was impressed with the ability of the Naos 55 to keep my gear dry. It carried well and held everything I needed for a winter 3-day trip in the Great Smokeys. The drybag type closure can be a little bit of a pain getting larger items in and out but worth it. We'll see how good it is after a few good years of use!

The Arc'teryx Noas 55 Pack is a great pack to use on longer trips. It can handle anything that mother nature has to throw. I used this pack on a 3-day trip and I loved it. I was able to carry everything that I needed and more without the worry of ruining anything because of water. I love the dry bag design of the bag as well. Not only does it make it a very secure bag, but it also makes it a very waterproof bag. On top of that, Arc'teryx has waterproof that top off the waterproofing of the Noas. This pack is also very adjustable, from the hip straps to the shoulder straps to the back support.

Got this pack for a trip across the US on my motorcycle which started April 1, 09.
I needed something waterproof to weather and larger than the standard motorcycle top cases that are really small. So I got this pack and just strapped it on top of my passenger seat and away I went...after 29 days on the road of which I backpacked 8 days-everthing inside the pack was always bone dry, thats riding and packing through snow, sleet, rain, 130mph winds on my bike with headwinds and 100mph wind with hvy rain. I actually used it to forde..more like swam across a swollen stream 3 times in Utah with the pack as my flotation device, I did use two tiny patches of duct tape at the zipper ends to ensure no water penetration to my map and trail book, not sure if that was necessary but better to be safe than sorry. When I travel motorcycle style I only take a bivy sack which means this pack was always outside in the rain, snow, sleet and sun for 25 of the 29 days and always dry. Only odd problem I had was 50mph wind knocked it over once during a stormy night onto its front and the pack just slide away like a tobaggon pushed by the wind, lol, started tying it down with paracord after that adventure. It was also great when staying at a hotel some nights as you can just throw the pack on and grab the bags out of my aluminum motorcycle side luggage all in one trip. The padding dries really fast and didn't get punky the entire trip. As far as harness fit, the shoulder straps lock onto a retagular patch of ? PTFE? or some kinda hard plastic located about between your shoulders and can be adjusted up and down and sideways which is great for narrow or people like me with wide shoulders. I'm not a professional backpacker but but after several thousand miles of hauling a rucksack around which I hated dearly, this packs really got me gassed up to do some serious backpacking, but, this time in comfort instead of using a pack from the lowest bidding Mil Spec contractor !

I love this pack. It's got all the features you need and none you don't. It's waterproof and bombproof. I found it to be super comfortable as well with some adjustment to the straps and waist belt.

This thing is AWESOME. Im about 5'6 and this bad boy fit wonderfully. The straps are like wrestling mat material which makes it very comfortable when your packin in all your boooz.... But really, you can pack in a huge load in the roll away main compartment, and the outside pockets have a nice amount of room for easliy accesing your "keep close" gear. I hiked in a pouring rainfall for 5 hours and your iphone will be just fine in this thing. Not a drop of rain on anything! This thing is like a gigantic, waterproof, dry sac.... Expensive, but you will never buy another pack again....

Good Backpack!!

I just took this pack down to Coal Pit's Wash outside of Zion NP and was impressed with how tight the pack holds everything in a minimalist design that is very durable and light. The 420D fabric is super bombproof and didn't rip at all on the rocks, cacti, and trees it brushed up against on the trek. I found the bladder adapter to be quite simple and effective as well for easy access to a drink of water. Overall, a great design for those quick alpine ascents and two night desert trips. I would not recommend the Naos 55 for any trips over 2 nights if you are taking a sleeping pad, tent, sleeping bag and cooking gear as it is a bit small for anything over a short jaunt. I would recommend the Naos 70 for anything else over 2 nights if you have a ton of gear. My only problems with the pack was the waist belt rubbing on my hip a bit, which was annoying but could be something to do wtih adjustments to the pack perhaps. Also, the side gear straps could be made a bit larger for adjusting to larger diameter tents (when packed), but I managed to squeeze it in there. Overall, this would be a great pack in coastal rainy climates or a super durable pack or mountainous/desert climates as well.

Took this on a canyoneering trip last summer and it did the trick. The straps weren't the most comfortable thing in the world, but the overall function of a 100% waterproof pack made up for it. Very simple, minimalist pack. Perfect for river trips, canyoneering, or fast and light hiking in wet climates.

This pack is pretty sweet! Lightweight, waterproof, comfortable, and super durable. I am really impressed with the construction of the pack. It’s not over loaded with straps or pockets that you don’t need. It holds all the gear I need for a trip, and it’s easy to get in and out of with the great roll top opening. This is just an all around bomber pack! No complaints from me.