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Gear Guy

Do sleeping bag "add-ons" really improve the bag rating?

I'm planning a trip to Tibet, and I'm looking for a bag in the zero to ten degrees Fahrenheit range. In addition to struggling with the age-old down versus synthetic issue, I'm also confused by the suitability of those Sierra Designs' down bags that include add-on top layers, such as their Buddy Rad. (They even suggest stuffing clothing in between the layers if it's cold.) Will this setup keep your whole body warm if the add-on layer only goes on top? Overall, I place great value on lightness and even more on compressibility, but I'm always wigged out about getting down wet. Matthew Boston, Massachusetts

A: Sierra Designs' Buddy Rad, and similar bags made by the company, does offer an interesting concept ( It's basically a zero-degree bag with a zip-off "lid" that can be removed when temps are 20 degrees or above. The result: A single bag rated from zero to 20. And it's a nice bag, at that, with 800-fill down and excellent construction. Weight is OK but not brilliant—at three pounds, 13 ounces it's heavy for a zero-degree bag, and at three pounds with the lid removed, it's heavy for a 20-degree bag. That's because of the extra fabric and zippers involved in the design. But it's not terribly porky, and the flexibility lets you be more comfortable—sweating less when it's warm, not breaking your teeth from chattering when it's colder. It is, however, pretty pricey at $475 (although if you shop around I think you'll find one for $400).

So, does it work? Sure—insulation is insulation. As you note, you can even add insulation by stuffing clothes between the layers. I wouldn't worry about your underside, as that insulation always get squashed anyway, which is why you need a good sleeping pad. As for your head, I'm sure the hood is plenty warm for zero degrees, but you can always throw on a hat.

As for moisture, how could a bag get wet when it's under 20 degrees? Any precipitation will fall as snow, so unless you're camped outside without a tent or bivy bag, the bag should stay plenty dry. I've used down bags in all sorts of snowy, sub-freezing conditions without much of a problem, although I will say that in conditions right around freezing, if it's snowing heavily, it's well-nigh impossible to keep everything dry. Still, reasonable camp-craft should ensure that your down bag stays dry enough to perform. Contrary to what I think has become conventional wisdom, down bags can actually absorb a fair amount of water before they really crap out on you.

My advice: Sure, give the Buddy Rad a try. You really won't go wrong.

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