On our very first "modern-day" backpacking trip, we took our goodness-knows-how-old, stupidly heavy (10+ pounds), two-person sleeping bag with almost non-insulating, collapsed synthetic fill. It was completely in line with our other gear.
Then we got at least a tiny bit smarter, before the second tirp, we bought two youth-size bags made by High Peak, weighing around 2.5 lbs. each, also synthetic-filled, but at least in brand new condition, so the advertised 20 degree rating was accurate. We barely fit in them, but they could be zippered together, and they worked considerably well. However, after my injury with the elephant-sized load in Mineral King, and our decision to slowly purchase the lightest possible version of everything, I started looking for a better option. We still used the two synthetic bags on a few short trips, including the Mini Trans-Sierra, but I was already researching other bags.
Honestly, I have no idea where I heard about Nunatak first and how I found them. It's a very small company based in Seattle, building ultralight down equipment where each item is completely custom and pretty much made to order. It's also stupendously expensive. The owner used to be a guy called Tom who had a reputation on several forums for being somewhat rude, but we was pretty OK with me. Not the best and most friendly customer service, but I can't really complain.
The bag I was looking for is not even a bag, it's a quilt, meaning it's open at the bottom. However, at around 2 pounds for the two-person version, it's unbelievable light, much lighter than anything else on the market. Oh, and depending on specs, it can cost upwards of $800. We didn't have that much money, but they have a clearance section on their site, sometimes listing prototypes or returned items for less than the full price, so I kept watching that. The patience paid off, just when I got paid for a big job, they listed exactly what we needed: a two-person Arc Alpinist in medium size, with Pertex Quantum 1.0 shell and 950+ down, somewhat overfilled, rated nominally at 20 degrees or a bit below. All this weighing in at 2 pounds and 1 ounce. I have to repeat this: two pounds and one ounce.
Also, it could be shipped right away, as opposed to the 2-3 month wait time for a regular order. It cost $600 plus shipping, and it didn't even include a stuff sack, we had too pay for it separately. The sack they shipped first did not compress the bag well enough, it was too big, so I had to mail it back and they sent us a smaller one. All in all the thing ened up costing around $650. Even years later, we still agree with Em: it was worth every single penny and it's one of our favorite pieces of gear.
...is pure bliss. Of course, like most quirky ultralight gear, it takes some getting used to. First of all, looking at the bag and the stuff sack, the first thought is: "There's no effin' way this will fit". But it does, actually quite easily, with room to spare. We could have gotten an even smaller bag and compressed it even more, but there's no point, the size you see in the picture fits the bottom of my Golite Pinnacle perfectly, and there's no need to damage the down more than necessary.
On this note, to extend the life of the bag, at home we store it loosly packed in a giant pillow case, and on the trail we ty to make sure it stays packed for the shortest possible time. As soon as the tent is up, we unpack the bag as well.
The Pertext Quantum is surprisignly soft and silk-like against the skin and the down feels like there are clouds inside. Really well-insulating clouds.
Sleeping in it and arranging all your limbs comfortably takes a bit of practice, but after a while, it comes naturally. There's a closed foot box, but further up, the quilt is open, held toghether by three thin, adjustable straps. However, there's enough quilt to tuck some under your body if needed. Depending on the temperature, the straps and the amount of tucking can be adjusted to the individual needs of the two people inside.
Most nights when it's above 20-25°, we both sleep in our short undewear with no socks and no extra layers. If it's above freezing outside, we usually leave the straps almost fully open and I even have my arms out. When it's really cold, we close the straps as much as possible and sometimes we wear socks and/or long undewear, but nothing very thick (for example, my long johns are Capilene 2 and Em's are Capilene 3). I think the coldest we ever experienced was in May 2014 at Kearsarge Lakes where it must have dropped close to 10°. We had a great sleep, not feeling cold at all. That's how great this bag is.
The Pertex 1.0 shell is not waterproof, but it's pretty water resistant, a few drops of condensation can easily be wiped off. We try to avoid getting it wet at all costs, and so far we've succeeded, but I can imagine that it's not a pleasant experience.
I even spent a night alone in the bag, when I took two friends to Mt. San Jacinto and slept in a tent by myself. It was just under freezing, as the bag is a bit too big for one person, but I wrapped myself in it completely and I was fine.
Nunatak changed owners since, and looks like they are pretty much making the same things. I only had one brief interaction with them - it seems they're working hard to improve customer relations and doing a good job at it. Also, I was told their bags now come with both stuff sacks and storage sacks (!). Great news.
Budget permitting, I'm definitely looking into buying more gear from them. We're especially keen on getting a Backcountry Blanket and maybe those really nice specialized jackets.