What’s the deal with sleeping-bag temperature ratings?
Dear Gear Guy, I longtime winter outdoorsman, but a winter and alpine camping beginner. I bought a -5-degree Polarguard 3D bag that I've slept in at temperatures ranging from 15 to 30 degrees in high-quality tents and on a (cushy) RidgeRest/Therma-Rest combo, albeit on snowand I always freeze, if not right away, then definitely by 3 A.M. I wear at least two layers, often my third, hat, etc. Short of wearing my outer layer (!!) or my belay jacket/pillow to bed, what gives? I just in kick-ass shape (no insulation layer) or just a total wimp who needs to buy a warmer, heavier bag? Or is there something about temperature ratings that I'm missing? Bill New York, New York
Temperature ratings are among the most misunderstood bit of nomenclature in the outdoor world. I myself have used phrases such as “this bag is conservatively rated,” or “this maker is a little generous with its rating” without so much as a single shred of objective data with which to back up such an assertion.
Which is a state of affairs I share with the sleeping bag industry. It’s all rule of thumb “X” inches of dead air should result in “Y” insulation value, or dummy “C,” when warmed and then cooled, should mimic human body type “D” and so on. The variables are endless: Individual metabolism, fat/muscle ratio, whether a person is tired or fresh, what they ate for dinner, and on and on.
Bottom line: For you, the Polarguard bag ain’t cutting it. For someone else, it might be fine. Certainly, it sounds like you’re doing all the right things. You have a good pad, you’re dressing warmly (ignoring the old saw, “you’ll sleep warmer if you go to bed nude!”), and wearing a hat to bed. It is true that eating a calorie-rich snack before bedtime can help; a Snickers bar or something like that can make a significant difference. Maybe keep a snack handythe metabolism of most people slows around 3 A.M. or so, which probably is why you’re waking up cold around then.
Otherwise, you just need a warmer bag. Or maybe a silk liner ($40 to $60) would add just enough insulation to keep you comfy.