But as the temps dipped into the 40's, I found myself regretting the decision not to bring a sleeping bag. I had all my warm layers on, but still shivered through the night and barely slept at all. That's when I resolved to invest in an ultra-lightweight sleeping bag for climbing trips, and ended up buying a Z-Packs 40-degree down sleeping bag (Full disclosure: Z-Packs gave me a discount on my purchase in exchange for writing a review).
Overall, I have been impressed with this bag. My 40-degree bag squishes down to about the size of two Naglene water bottles put together, and Z-Packs sends the bags out with lightweight and strong Cuben fiber stuff sacks.
The bag is filled with 900-fill down inside a ripstop nylon shell and holds true to its temperature ratings--it's kept me warm and cozy on trips to climb Mt. Russell, in the Emigrant Wilderness, and on multiple Mt. Baker summit climbs. The 40-degree bag is incredibly lightweight at just 11.4 ounces, and it's also available in 30-degree, 20-degree, and 10-degree versions. These are great bags for ounce-counting climbers operating in environments where they can depend on staying dry (it's not water-resistant down, so if you've got rain in the forecast stick to a synthetic bag).
One of the main ways Z-Packs able to make the bags so light is by cutting out any extraneous features. Since a lot of people don't use the hoods of their sleeping bags unless it's REALLY cold out, they cut out the hood altogether and the bag just goes up to your shoulders and cinches down with a drawcord. The zipper also only goes 3/4 of the way down and is designed for you to lay on top of it instead of using a draft tube to trap heat.
The cuts to these features means it's not most tricked-out bag with all the coolest design items. But it's simple, light and has what you need, which for minimalist climbers is all you ask for.
--Shelby Carpenter, AAI Instructor and Guide