Obviously, a double sleeping bag is the best choice for couples; another advantage is that most double sleeping bags can be unzipped apart and converted into single bags. You can also usually zip together two single sleeping bags, but if the two bags aren't the same make and model, the zippers may not fit together to convert two bags into one.
The flannel-lined Coleman Hibernation 40-Degree Rectangular Queen Size Sleeping Bag (*Est. $70) is only 75 inches long and weighs 15 pounds, quite a bit more than zipping together two of the 5.6-pound L.L.Bean Camp Bags discussed earlier. The less expensive Coleman Hibernation double sleeping bag carries a five-year warranty, though, and gets mostly positive reviews from owners at Amazon.com. One owner notes that the zipper sometimes snags, but this is typical of rectangular bags since the zipper goes around a 90-degree corner.
Owners reviewing sleeping bags at Amazon.com like the 78-inch-long Slumberjack Bonnie & Clyde 40-Degree (*Est. $85), which comes with two pillows. One-half of this sleeping bag has an extra pound of insulation, so when the two bags are zipped together you can use the more insulated layer on the bottom on warmer nights. If you separate the bags, one is warmer – nice if one person in the couple "sleeps colder" than the other. The warranty is for just one year.
Cabela's also includes pillows with its 84-inch-long "Adam and Eve" double sleeping bags, which get very good reviews from owners. Cabela's Warm-Weather Adam & Eve (*Est. $130) is insulated with DuPont Thermolite synthetic fill and rated to 40 degrees. The warmer three-season double sleeping bag is the Cabela's Northwoods Adam & Eve II (*Est. $170), rated to 15 degrees. It's insulated with 8.5 pounds of DuPont Quallofil insulation, which has more loft and insulating power than Thermolite. Two offset layers of double insulation prevent cold spots, but the extra insulation and heavy cotton twill cover brings the total weight up to almost 20 pounds.
Cabela's Ultimate Adam & Eve (*Est. $290) is rated to minus 15 degrees, but weighs less (15.5 lbs.). This is because it combines one single sleeping bag insulated with 3.5 pounds of lightweight down filling with another single sleeping bag insulated with four pounds of DuPont Quallofil. The down filling requires a nylon taffeta lining, which is not cozy like flannel, but most people use a liner anyway.
The flannel-lined Teton Sports Mammoth 0-Degree (*Est. $110) double sleeping bag carries a lifetime warranty and gets good reviews at Amazon.com. It's plenty big – 62 inches wide and 94 inches long (including an optional face cover), and owners say you can easily tuck a child between two adults. Unlike the double sleeping bags discussed earlier, this one doesn't zip apart into two singles. It does have side zippers for ventilation and for getting in and out.