Will a bivy keep me warm and protect my bag?

I’m considering buying a bivy to add warmth to and protect my Mountain Hardwear Phantom 32 sleeping bag, which I chose for its light weight. I cp mostly in lean-tos or other minimalist shelters, and when the temp gets down to 35 degrees, I get chilled. I’ve tried liners for warmth and to protect the inside of the bag, but they’re too confining. Any thoughts on the Mountain Hardwear Conduit Bivy? Or do you have other recommendations? Cheryl Melrose, Massachusetts

A: Let me get this straight. You bought a 32-degree bag (the Mountain Hardwear Phantom 32—$245;—is rated to 32 degrees, weighs one pound, five ounces, and has down fill), then immediately began taking steps to add to its thermal qualities? I’ll discount the save-the-lining theory; it’s true that you need to keep a bag’s lining clean, but wearing long underwear and the occasional laundering takes care of that. To put it another way, I have never seen a bag lining fail from “wear."

Western Mountaineering’s Apache Super MF

Apache Super MF

So, I guess what I’m working up to is the question of why you didn’t just buy a warmer bag. Western Mountaineering’s Apache Super MF, for instance, is rated to 15 degrees, weighs two pounds, one ounce (or, about the Phantom plus a liner), and retails from $350 to $380 depending on length.

That, however, would appear to be a horse that has left the barn. What to do about the Phantom? A liner of some sort isn’t really going to work, as it’s a very trimly cut bag and, as you mention, it will be too confining. Seems to me the best solution is to upgrade your long underwear to at least a medium-weight (REI Midweight MTS bottoms and tops are $30 each; or even expedition-weight (Duofold Varitherm bottoms and tops are $37 each; Along with gloves, socks, and a hat, that’s good start to keeping you warm.

A bivy bag works, too, albeit at fairly steep expense ($110 for Mountain Hardwear’s Conduit SL Bivy) and extra weight (one pound, two ounces—same as your bag!). Mont-Bell’s Breeze Dry-Tec U.L. Sleeping Bag Cover ( uses a somewhat similar material, costs the same, and weighs half as much. There is some risk, in certain weather conditions, that moist air escaping from your bag will condense inside the bivy. But you will be warmer.

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Filed To: Sleeping Bag Accessories
Lead Photo: courtesy, Western Mountaineering
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