What are the advantages of a double sleeping bag?

Question

In the context of a long hike (AT, PCT, CDT, LT, etc.):

What are the advantages and disadvantages of double sleeping bags over two individual sleeping bags? How do they compare to single sleeping bags that can mate?

Which solution can keep you warmer? How much warmer? Which solution yields a lower packed weight?

Essentially, what are the main differences and criteria that should be taken into consideration when choosing a two person sleep system?

Answer 1

The only real difference is that in a one piece double you don't have zips so the insulation is evenly distributed. The zips add some weight over a one piece but not much - it also won't pack quite as small but has the advantage that it can be split across two packs.

Where you have zips, the insulation has gaps. So if you are going somewhere really cold, you might want to go with a one piece.

I far prefer the two pieces that mate together because I carry a much higher temperature than my wife so I like the fact I can unzip and roll my side down to my waist if need be.

Also easier to pop in the washing machine :-)

Answer 2

This answer is mostly on comfort, for more technical/practical considerations, please consult Rory's answer above.

I can express opinion about this double sleeping bag.

• Cheap, which affects it's other characteristics.
• Weights 3.6 kg, takes up most of the space in a large (60+)l backpack.
• Warmth is about the same as my single 3-season sleeping back.
• Putting insulation pads underneath is a little awkward, as the sleeping bag is quite large.
• Sleeping in the correct temperature (maybe down to 5 degrees Centigrade) is very comfortable. It feels like a large bed, in which one can move freely. Actually the bag can probably fit 3 persons.
• Because it is so spacy, there is some air movement inside (i.e. less warm than an individual mummy bag), which can be good or bad.

Overall, it is equivalent to two separate sleeping bags. On a serious journey I would not take it, as

• Finding even ground for two (actually more like three) sleeping bags is harder than finding two individual good spots to put the sleeping bags.
• None of the advantages of mummy-style sleeping bags.
• At the end of an exhausting day one rarely has the energy to hug the sweaty and filthy other person.

On the other hand, for leisurely weekend trips in warm weather this provides the ultimate comfort and intimacy with the loved one.

Answer 3

There can be a slight weight savings for a double bag over two single bags. This is difficult to fully calculate, especially if one person sleeps warmer than the other or if there is a height difference (e.g., one person needs a long bag and the other a short bag). There can also be a comfort advantage, but it really depends on how narrow the double bag is. I have a wide single bag for car camping which probably qualifies as the "spooner's only fit" in your link which is no where near as comfortable as mated single bags, but definitely the lightest option. My real dislike of mated single bags are the middle zippers and separate foot boxes.

For long hikes there are a couple of serious disadvantages. First, a double bag means you must camp together every night. It also means you need to stay in closer contact on the trail as one person is not carrying, what is in my opinion, the proper emergency gear. Further, if the bag gets wet, there is no backup (and probably a lot of blame). I would also be worried about drying the bag out in town since getting a double bag in a dryer might be problematic. There is also the issue of weight/volume distribution.