I can't say enough good things about this pack. I got it to replace a heavier pack setup, but wanted a material that was still durable. I really love the xpac material, and the best part is I don't need to worry about trying to put a rain cover over it. I will say, there's a drain built into the back along the bottom side, so if you're caught in a downpour you may still need to cover the pack to prevent anything from getting wet. The drain hole is approximately 1", so I doubt much water would find it's way in the bag, but I can't say for sure. An obvious way around this is to use a dry bag for your items. I however am loosely packing my sleeping bag in, since this is a frameless pack. That alone is the biggest question I see.
The hip belt is adjustable. It also has dual buckles so you can get a more custom fit on your hips, although it doesn't adjust quite as easily as a zpacks with the "Y" adjustment strap. You will need to play around with adjustments ahead of time. One feature of the waist belt I really like is the tension straps pull from the outside in, which is supposed to be more ergonomic. My other pack does not have this feature, and I can definitely tell the difference.
The pockets on the hip belt don't seem to be as roomy as the ones on the other cheaper backpack offered by 3F, but I am still able to squeeze my iphone 7+ in, barely.
The pocket in the back has some stretch to it, but not a lot. I can fit a puffy in it, with room to spare. Probably have room for a couple hat, gloves, and lunch/snacks for the day.
The side pockets are fairly large, but not overly deep. I can fit my jetboil in, but it's a somewhat snug fit once the main pack is full. I can easily get two smart water bottles in one pouch. Once the shock cord is cinched everything is pretty much locked in.
The main part of the pack. I'm able to get my 20 synthetic sleeping bag, 3f 2 man tent, ground sheet, and a bear vault BV500 into the pack. I probably have room for one extra set of clothing, although I haven't packed that into it yet. Obviously the bear can takes up a lot of room. I would say close to half of the useable space, but I could still stuff some smaller things around it. With all of these things I mentioned my total base weight is 16 pounds. That with the bear can loaded with 4 days worth of food for 1.5 people( It still has more room, and I'll be packing food for myself and another friend). Because the pack is loaded as such, I'm not able to roll the top down quite as far as the pictures displayed , but I can still get 3 solid rolls out of it, and can either secure it with the side straps or clip the top together like a typical roll top dry bag.
When you receive the pack 3F supplies it with the clear air pocket frame. It's a joke. This might be the biggest waist in the whole pack. I immediately took it out because it's no more than a glorified plastic bubble. I'm pretty sure it would pop if fully packed, and if it didn't it could very easily get punctured. With that said, it's gone. The pack does have spacer foam padding on the back, which a lot of ultra light packs don't. I could see it as added weight, but I do feel it adds a bit of structure to the pack, considering it's a frameless pack. I don't see any reason to keep the straps on the inside of the pack that previously held this "frame", so they will probably be going, and all of the compression straps can be shortened significantly.
I ordered the Large, and I'm about 6'3", wear 36" pants, weigh 260. I'm not a small person, and I found the adjustments within this pack capable of providing a comfortable fit. If I could customize one thing it might be to have "S" straps. I have pretty broad shoulders, and a big chest, so I feel like those would help with some fitment around my chest to armpit regions.
I've worn the pack loaded as mentioned around the house while cleaning and doing other chores. I never once thought it was uncomfortable. Even with the hard bear can I was able to smash my sleeping bag and other soft items around to create a comfortable fit.
Even with a few of the tweaks and minor adjustments I'm really happy with this pack. It's more money than the other pack, but made with a durable waterproof material which in my opinion makes it a good buy. A lot of other packs of this caliber and material will be 1.5 to 2 times as much