Mummy bags can indeed be confining, particularly if youre not used to them. But you understand why they exist, Im surethe 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.
That said, plenty of bag makers understand that a roomier bag is often more comfortable. And todays light materials mean you dont 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. Its also incredibly light at two pounds, 11 ounces. Alas, you pay a pretty penny for these features.
Its a little tricky to find full rectangular bags that arent enormous and bulky. But if youre car-camping, take a look at the Slumberjack Big Timber +10 ($60; www.slumberjack.com). Its rated to 10 degrees and is a true rectangular bag. Its not low in weight, though, tipping the scales at nearly 10 pounds.
Myself, Id go with the Big Agnes, and call it good
Check out this years more than 400 must-have gear items, including a comprehensive sleeping-bag section, in the 2006 Buyers Guide.