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I'm buying a double sleeping bag for travels with my girlfriend.
Parameters (of the bag, not the girlfriend): 1500g of goose down, 680 in³/oz (393 cm³/g), 90/10% down/feather, rated to -9...-15°C T-comf when two people are inside.

  • Question one: Would I be comfortable sleeping in it alone or would the extra inner space sap my warmth? What if I hogtie the bag with a bungee/paracord?
  • Question two: what would be the (approximate) T-comf for such solo sleeping?..

NOTE RE: ZIPPABLE BAGS
Yes, I had had thought about them. However, there are a few cons:

  1. They have to be Left/Right, i.e. matching. The company that I'm buying my bag from doesn't produce matching sleeping bags.
  2. I've owned zippable bags and checked out some. All of them had one problem: the zip would stop at the shin level, basically creating two separate spaces for feet. That could be uncomfortable to sleep in (a double mummy-type bag would have a tapered but single feet space).
  3. Two bags are more expensive than a single double bag, and we're talking down which already has a hefty price tag
  4. Two bags (usually) weigh more than a single bag from the same model range
Alexander
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7 Answers7

81

In my experience, most standard single sleeping bags, are built so you can zipper them together to make a double. They are designed to zipper to an identical/matched bag, so don't count on buying to different bags and have them work together.

Instead of buying a dedicated double bag, buy a matched pair that can be joined. Google sleeping bags that can be joined together or sleeping bags that can be zipped together

When you are sleeping alone, no problem.

When you are sleeping together no problem.

When you are in trouble and she makes you sleep alone, no problem.

James Jenkins
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    Another point for your "pros" list (from experience): When you get too hot and need extra ventilation and exposure to cool down, no problem. My wife and I have both a dedicated double bag and a pair of attachable singles. Two vents are better than one. – Loduwijk Aug 19 '19 at 17:46
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    Isn’t there usually a left and right side for a pair of sleeping bags which can be zipped together? I.e. it’s a matched pair, not identical bags. – Michael Aug 20 '19 at 12:02
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    @Michael when you turn one over, the left becomes the right, and they zip to each other as the top of one to the bottom of the other. – James Jenkins Aug 20 '19 at 12:04
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    @JamesJenkins: Don’t they usually have a dedicated top and bottom side with “hoods” for the head? I’ve been using quilts for years, but I dimly recall this from my sleeping bag days. – Michael Aug 20 '19 at 12:07
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    @JamesJenkins it depends on the model. Mine are joinable if -- and only if -- paired left/right, since they have a hood. – Davidmh Aug 20 '19 at 12:26
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    Having used both a pair of zipped together singles and a dedicated double, I really appreciate the features of the double and would prefer it over two zipped-together singles both when with my wife, and would prefer it over a single when solo, unless my solo trips were really weight or space sensitive. Sleeping alone in a double is like having a king bed all to yourself, it's great! – dwizum Aug 20 '19 at 15:34
  • Just saying my husband and I have zip together bags but we get too cold when they are, and just use them seperately now. +1 though still a good option. – Aravona Aug 21 '19 at 08:36
  • Another useful advantage of two separates is that they can be used one inside the other for those really cold nights alone. – Tim Aug 21 '19 at 14:00
  • Bear in mind, there aren't that many different zipper manufacturers and models. Many sleeping bag brands will use the same zip components and different models can sometimes work together. I've tested it several times in the years I spent working in outdoors retail. – Gabriel Aug 28 '19 at 19:06
26

The parameters of your girlfriend would matter depending on the ratio of 'space' occupying, but let's ignore that for now.

I would put a cord or something around it to minimize the space; air needs to be warmed up too. You should try to tie it in such a way, that you have on one side a 'triple' layer (half of the bag bent, so something like this

/--------------\    Top
|     You      |
| /------------/
| \------------\ 
\--------------/   Bottom

<-----Width---->

instead of the normal situation

/----------------------------\  Top
-       You           GF     |  GF = Girlfriend
\----------------------------/  Bottom

<------------Width----------->

If you have a thick (air) layer under you, you can keep the three layers of the sleeping bag on top of you, if you have a thin layer under you, since most cold is going through the ground, put the three layers of the sleeping bag underneath you (like in the picture).

Also you can fill the sleeping bag with clothes (they will be warm in the morning), water or other drink, and even your shoes (put them in a plastic bag).

Michel Keijzers
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  • @Loduwijk I had two lines too much (so I removed them), and added orientation. And yes, it's the view from the head or foot (thus width, not length). – Michel Keijzers Aug 19 '19 at 18:53
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    Very nice graphics - though the space between "You" and "Girlfriend" is a bit generous :) – imsodin Aug 19 '19 at 20:41
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    @imsodin Maybe Michel should add a comment like "(Not to scale)", just to make sure that he doesn't imply that the girlfriend is more than three times as wide as the "you" ;-) – anderas Aug 20 '19 at 06:06
  • @anderas I used the abbreviation... I can't help that ' Girlfriend' has much more characters than ' you' – Michel Keijzers Aug 20 '19 at 08:16
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    @MichelKeijzers Now it looks like a very slim girlfriend :-P I hope it was clear that I really was just kidding ;-) – anderas Aug 20 '19 at 08:44
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    @anderas ... I know :-) ... besides, it's not my gf, so it's hard to make a good picture, for that the parameters of his gf should be added. Also depending on both moods, they might be closer, or further away from each other ... or on top of each other. – Michel Keijzers Aug 20 '19 at 08:50
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    It’s not like the space usually occupied by the GF will create a void when she’s not there. The bag is going to lie flat around you, like using a quilt. I think a cord would just unnecessarily compress the bag. I don’t think folding it into a triple layer will work properly. – Michael Aug 20 '19 at 12:09
  • @Michael I never tried it, but if someone doesn't move too much while sleeping, it should stay quite well. – Michel Keijzers Aug 20 '19 at 19:35
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    I'm accepting this answer for: 1. Being the first :) 2. Nice ASCII art. 3. Comments. And, on a more serious note, for this sentence: "Also you can fill the sleeping bag with clothes (they will be warm in the morning), water or other drink, and even your shoes (put them in a plastic bag)." This is absolutely brilliant, I haven't thought about it! – Alexander Aug 28 '19 at 15:15
  • @Alexander glad I could help you. Btw, I did it quite some times, used to hike every year in the winter for 2 days, and putting my clothes inside the sleeping bag while it was freezing outside gave me (sort of) warm clothes in the morning. – Michel Keijzers Aug 28 '19 at 15:21
  • @Alexander Make sure to come back with your feedback of how it works out because from experience any small unused space creates cold drafts when one moves around inside the bag. Even just curling up my knees slightly in my winter mummy and having the toe box collapse for some time will make it freezing cold when I move my feet back down in it. – Gabriel Aug 28 '19 at 18:06
  • @GabrielC. It works best (or only) if you don't let cold air inside the sleeping bag, thus sleeping also with your head inside the sleeping bag, so you can just leave a small air 'gap' to let some fresh air in to breath. – Michel Keijzers Aug 28 '19 at 18:22
  • @MichelKeijzers No need to let cold air get in. If part of the sleeping bag cavity collapses, it doesn't get warmed by body heat. That part of the sleeping bag will get cold and cool down the air when it is filled again. I know from first hand experience. – Gabriel Aug 28 '19 at 18:39
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If the bag is laid flat like it would be for two people, it will not be nearly as warm. Basically you are doubling the effective surface area in which to lose heat relative to a single person sleeping bag. If you fold the bag on top of you, you will be keeping the surface area about the same as a single person bag and effectively doubling the insulation. This will be very warm if the extra material stays on top of you.

Keeping the extra insulation on top of you is going to be difficult. Trying to tie yourself in the bag so that the multiple layers do not flop around seems like a bad idea. Putting the extra layers below you leads to them being compressed and losing most of their insulating properties.

Your best bet is to probably buy two bags with mate-able zippers. I tend to suggest that when men and women are buying a pair of sleeping bags to buy the woman a warmer (lower temperature rating) bag than the man. This tends to make the couple sleep more comfortably and gives a greater range of comfort when the bags are detached.

StrongBad
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5

Zip-together bags would be the best solution but if you already have a double then just fold the sleeping bag in half and sleep in the top half with the other half underneath you. You get extra cushioning and extra insulation between you and the ground and your weight will keep the sleeping bag (mostly) folded.

Tim B
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5

It might be a little colder but I don't think it would be so much colder as people are thinking.

It's a bag, not a box or a balloon. The unused area should fall flat leaving little extra air-space inside for you to have to warm.

You will feel cool material if you turn in your sleep though. Depending on the weather that might even be a good thing.

Leif
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    Good point with that sentence: "You will feel cool material if you turn in your sleep though. Depending on the weather that might even be a good thing." – Alexander Aug 28 '19 at 15:23
  • If it's winter cold, what you describe is the best way to spend an entire night unable to sleep or getting woken up constantly. I'm a restless sleeper so to make sure I can't move in my sleep and curl my legs (which is difficult but doable in a mummy bag), I fill the void between my legs with clothing because constantly having my feet exposed to cold air in the toe box kills my sleep. My bag isn't too long for me either, it's the perfect size and it still happens. – Gabriel Aug 28 '19 at 18:13
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I'll second the recommendations to buy bags that can zip together. We have the older North Face Cat's Meow, and they work well for my ultralight distance hikes, and for family camping.

While you can zip things down, remember that compressing loft is your enemy. Use a light touch.

Jonathan
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  • Can you clarify your last two sentences because I really don't understand. – Gabriel Aug 22 '19 at 19:12
  • The loft/poofyness creates insulation. Don't flatten your bag. – Jonathan Aug 23 '19 at 20:07
  • No, not that, that's evident. Why use a light touch. That's what makes no sense to me. And how does flattening the bags relate to zipping them together? It's all weird. – Gabriel Aug 23 '19 at 22:40
  • "Zip things down", not "zip things together" @GabrielC. What Jonathan is referring to is my proposal to hogtie a double sleeping bag :) – Alexander Aug 28 '19 at 15:14
  • @Alexander Then the answer requires a good rewrite because it's much too vague. – Gabriel Aug 28 '19 at 15:31
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Sleeping solo in a sleeping bag that's too big can be a miserable experience provided the night is cold enough to be marginal for the temperature rating.

My family still carries the vivid memories of a cool spring night (about 4 Degrees centigrade) when our then 11 year old daughter had forgotten her sleeping bag for a sail training camp. My husband decided to give her his own, and went to bed knowing it would be a long and chilly night for him. Little did he anticipate that our daughter wouldn't be much better, the vast and roomy sleeping bag felt like it just wouldn't warm up, and any movement just made things worse.

Unfortunately, neither of them communicated how uncomfortable they were, lying shivering in their respective tent compartments, trying not to stir in order not to wake the other (lying awake equally shivering through the night).

The following night I could join the trip and bring the missing sleeping bag along, the remaining nights both were comfortable again in their fitting equipment.

All sleeping bags involved were rated to -10 iirc.

Tatjana Heuser
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