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Thinking About Sleeping Bags – How Light is Too Light?

When I return from a pack trip I often reflect a bit on how my equipment did and did not work, and on how I might tweak my setup. One issue that always concerns me – and more so as I get older – is the balance between weight and functionality. This is especially important with core pieces of gear like the sleeping bag.

For the past couple years I have used the excellent Marmot Helium sleeping bag on most pack trips. Marmot uses high quality down and careful design (a half-zipper, for example) to provide a 15-degree bag that weighs only about two pounds and stuffs quite small. This is a fine piece of gear and, along with most other reviewers, I have only good things to say about it.

But do I really need a 15 degree bag for summer backpacking in the Sierra Nevada, where the temperature only very rarely falls to freezing? Not really. Some years ago I purchased an early model of the Marmot Arroyo sleeping bag. (Newer models of the Arroyo are available and appear to have been updated and improved.) This bag also uses the premium, high-lofting down, but it minimizes weight with a fairly tight cut and by minimizing the insulation to the point that it is rated only to 30 degrees.

On this past week’s quick trip into the Young Lakes Basin in the Tuolumne Meadows backcountry of Yosemite National Park I decided to take advantage of warm conditions and use the Arroyo bag again, after having pretty much switched to the Helium for the past couple of summers. And the results? Pardon the awful pun, but I’m going to say it was a mixed bag.

  • The Arroyo is about a half pound lighter than the Helium. Even more important, it packs down into an almost unbelievably small package – about the same size as a typical down jacket. Since I was also using a fairly small and very light Gregory backpack on this trip, the difference in packed size is significant. (This is especially true when the lighter, smaller sleeping bag is one element of a system that includes a small bivy sack rather than a tent, minimized clothing, and so forth.)
  • As expected, the Arroyo is not as warm. While an inch or so of insulation seems like it should be enough in relatively warm conditions, the thickness measurement doesn’t tell the whole story. A sleeping bag does not drape perfectly over the body nor maintain the same thickness everywhere. For example, with a bag like this I find that the down moves away from pressure points across the my body. I find that I tend to feel the cold at these spots (e.g. – hips and shoulders) , and I felt that my feet were less warm.
  • Because of the “not as warm issue” with a marginal bag, you need to pay more attention to maximizing warmth if you want to be comfortable. In my experience, all of the following can help. When unpacking the bag allow it to fully loft, and redistribute the down to the upper section – down under your body does no good at all. Wearing the right clothing in the bag can extend its range: I wear a pair of light long underwear bottoms and tops and socks, and I may add a light beanie if it really gets cool. I also carry the 11 ounce Western Mountaineering down Flight Jacket, and I can use it inside the bag to buttress those thin spots if I’m still not warm enough.

There is one other issue that I discovered over the years of using the Arroyo. Down sleeping bag loft seems to decrease over time. This seems logical and unavoidable if you think about it a bit, but it is a factor that I really did’t notice until I used the Arroyo for several years and in conditions where its insulation is marginal. Over time I’ve noticed a decline in the loft of the bag and find that a barely adequate bag can become inadequate on occasion.

Bottom line: Would I recommend the Arroyo or similar bag? My answer is a qualified “yes.” While a lighter/smaller bag will not make a huge difference in pack weight all by itself, if you take a similar approach to all of your gear you can make significant reductions in weight and bulk. Depending on where and how you travel, this can make a difference. (In my case, it is important because I’m far less amenable to carrying 50-75 lb. packs than I was a few decades ago… and because I now carry quite a few pounds of photo equipment into the backcountry.) But recognize that you’ll have to approach the task of keeping warm in marginal conditions more carefully, and you’ll want to think of your lightweight bag as part of a sleep system that also includes weather protection and additional clothing. I strongly recommend against using a marginal bag if you are new to backpacking – wait until you are a fairly experienced backcountry traveller who is willing to make some compromises in comfort. Beginners will be far better off with a bit more margin for error when the unexpected happens – a cold snap occurs, they accidentally get too wet in an afternoon storm, and so forth.


July 12, 2008 - Posted by | Commentary

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