The label on the sleeping bag said it was good to "20 below," so why were you shivering through the night when the air temperature only dipped to 15°F?

Kelty PolarGuard 3D synthetic
sleeping bag wards off winter's chill
in the Colorado highcountry

Welcome to the esoteric, arcane, and downright confusing world of sleeping bag temperature ratings. No other topic is guaranteed to generate as much cynical laughter among outdoorspeople, unless it's Smoky the Bear's role in forest fire policy.

	Buy the Warmth You Need

You would expect that when purchasing a bag that claims to be rated to 30°F it will keep you warm down to 30°F, right? After all, you expect as much from a 40,000-mile tire purchased for your car, and that tire costs a lot less — and arguably performs a more vital function — than a nylon cocoon stuffed with spun fiber or goose down.

Yet, in the field — or forest, or atop a glacier — that 30-degree bag can leave you cold well shy of its stated performance rating. Why are sleeping-bag temperature ratings so unreliable and what do you need to know about them to select a sleeping bag that can get you through the night comfortably? Read on.

Buy the Warmth You Need Pegging temperature ratings may be an inexact science, but a few general guidelines apply when shopping for a sleep sack. Set your temperature limit. Figure out what's the absolute minimum temperature at which you'll likely use the bag. Take into account cooler temperatures at night at higher altitudes and latitudes. Err on the warm side. When did you last hear someone complain about being too warm at night? Can't decide between a 20-degree or a 25-degree bag? Go for the 20. Exceed your budget. When people finally break open their wallets and buy a decent bag, it is usually after a succession of unsatisfactory purchases. Spare yourself the buyer's remorse and the uncomfortable nights, and make your first bag a quality bag.

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