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Mummy bags can indeed be confining, particularly if you’re not used to them. But you understand why they exist, I’m sure—the trim cut weighs less than a semi-rectangular or rectangular bag, and the snug interior space conserves heat by reducing the bellows effect when you thrash about.

Big Agnes Mystic 15 sleeping bag

Mystic 15 sleeping bag

That said, plenty of bag makers understand that a roomier bag is often more comfortable. And todayÂ’s light materials mean you donÂ’t pay a big weight penalty. The Big Agnes Mystic 15 ($299; www.bigagnes.com), for instance, is a 15-degree bag with 775-fill down insulation that has a roomy semi-rectangular design. It eliminates the insulation at the bottom of the bag, which gets squished anyway, and you insert a sleeping pad there to keep the chill from coming up from the ground. The weight, at two pounds, four ounces, is exceedingly competitive.

One of the really great semi-rectangular bags out there is the Western Mountaineering Ponderosa MF ($395; www.westernmountaineering.com). It has lots of super-high-quality 850-plus down fill, and likely could keep you warm well below its stated 15-degree rating. ItÂ’s also incredibly light at two pounds, 11 ounces. Alas, you pay a pretty penny for these features.

ItÂ’s a little tricky to find full rectangular bags that arenÂ’t enormous and bulky. But if youÂ’re car-camping, take a look at the Slumberjack Big Timber +10 ($60; www.slumberjack.com). ItÂ’s rated to 10 degrees and is a true rectangular bag. ItÂ’s not low in weight, though, tipping the scales at nearly 10 pounds.

Myself, IÂ’d go with the Big Agnes, and call it goodÂ…

Check out this yearÂ’s more than 400 must-have gear items, including , in the 2006 BuyerÂ’s Guide.