Gear Guy

Can I combine two sleeping bags for cold-weather camping?

I was thinking about combining my expandable Mountain Hardwear Galaxy SL sleeping bag with the maker's 40-degree Down Upgrade bag. What do you think about combining these two sleeping bags for a Denali summit attempt? Rob Boston, Massachusetts


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I think that combining bags can be an excellent idea. Your Galaxy SL (rated to 15 degrees, $305) is a good cool-weather bag that, with a little help, can become a good winter bag. One easy alternative: simply add a vapor barrier liner (usually about $30). If you’re not familiar with those, they’re simply a light bag of coated nylon that goes inside the main bag. Because they’re coated and waterproof, they stop evaporative cooling (the cooling effect you feel when you blow on a damp arm). That alone will lower the temperature rating of a bag by five to ten degrees. Wear some warm clothing to bed and the Galaxy becomes a zero-rated bag.

Or, as you note, the Galaxy’s expansion feature (a zippered gusset along the side allows the user to add up to eight inches of girth) gives you room for an extra insulation layer. Mountain Hardwear’s Down Upgrade—essentially a light down bag that can be inserted or zipped inside another bag—sells for $180. By itself it’s rated to 40 degrees. What it would add to the Galaxy’s temperature rating is a little hard to estimate, but I think it’s safe to say the Galaxy and the Down Upgrade would work well down to minus five.

Good enough for a Denali summit attempt? Probably not. For one thing, the combined bags will weigh nearly six pounds, and you’ll be carrying plenty already. For another, a bag rated to minus 20 must be considered the minimum up there. I think you’re going to have to review your trip budget and consider purchasing a bag just for this trip. But you needn’t spend a ton—L.L. Bean makes a good quality, minus 20 down-filled bag that sells for about $350. Or, if you want to splurge, get a Western Mountaineering Big Horn Super MF (minus 20, $530). Both weigh less than four pounds, a load difference for which you’ll be grateful. And, that vapor barrier liner will work well with both, adding to the temperature range if it gets REALLY cold.

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