Last Updated on 21/01/2022
In this article, we answer the question of whether you can and should use a sleeping bag inside a sleeping bag to theoretically double the warmth. You will learn how to maximize warmth using two sleeping bags inside one another and the potential downfalls of this sleeping bag idea.
Camping in cold weather requires a warm sleeping bag that is rated to match the temperature you’re camping in. You can choose a down-filled sleeping bag that is rated down to -40 degrees but costs over $1000. You could also choose a synthetic sleeping bag rated to -20 degrees but weighs over 3 kg and fills your entire backpack. Or you can consider other options like using two sleeping bags together.
Other alternatives include adding a sleeping bag liner for a few extra degrees of warmth, wearing base layers to sleep in, wearing down filled clothing to sleep in, or doubling up on the sleeping bags and putting one inside the other. But is there enough space, and will it even work? Let’s find out.
Can You Put a Sleeping Bag Inside Another Sleeping Bag?
You can absolutely put one sleeping bag inside another sleeping bag however there are a few considerations to make sure it doesn’t get too tight and restricted. The shape, size, and insulation type of the sleeping bag all influence being able to double up your sleeping bags. Here are some of the considerations in more detail:
Shape
Sleeping bags come in two basic shapes; rectangular and mummy-shaped. When you are putting one sleeping bag inside another you need to make sure that the shapes match. If they don’t then you should have the rectangular sleeping bag on the outside as it has more spaces inside for a second sleeping bag.
Insulation
Sleeping bag insulation also only has two options which are synthetic insulation and down-filled. There are pros and cons to both types of sleeping bag insulation however the key points to consider are loft and compression. Yes down compresses are much smaller than synthetic insulation but it also relies on loft to perform effectively. A double-edged sword.
So down sleeping bags will fit inside each other easier than synthetic sleeping bags but they will not perform as well as or maximize warmth. The best combination here might be to use a synthetic sleeping bag inside a down sleeping bag to get the best of both worlds.
Size
The consideration with size when combining sleeping bags inside each other is how tall and wide you are. If you are tall or wide around the waist then the last thing you want is to reduce the space inside your sleeping bag.
While it is not that common, many of the top sleeping bag companies will offer regular and large sleeping bag lengths. Obviously, the larger of the two need to be on the outside if this applies to your gear.
Temperature Ratings
Sleeping bags will often have a temperature rating that the manufacturer has tested its thermal qualities down to. This is often given as a range of comfort to the extreme. If you can find out the comfort temperature range of both sleeping bags you can roughly work out how warm the combined sleeping bags will be when inside one another. Temperature ratings are just a guide but provide useful information to base your decision.
Breathability
Combining two sleeping bags can have the issue of being too warm which can lead to sweating during the night. Sweat cooling in cold weather is one of the easiest ways to catch hypothermia so it is important to stay breathable. Basically, if your sleeping bag has a DWR coating then you should use that on the outside and avoid doubling up two sleeping bags if they both have waterproof shell fabric.
Benefits to Using a Sleeping Bag Inside a Sleeping Bag
Okay, so we know that you CAN put a sleeping bag inside a sleeping bag but should you? Here are some of the reasons why we think it might be a good idea:
Warmth
The number one reason anyone would even consider putting sleeping bags inside sleeping bags is to add warmth. Using a sleeping bag inside another sleeping bag can theoretically double the comfort rating of a single sleeping bag. If you thought your down sleeping bag was warm before, try doubling it and you will feel as snug as a bug.
For example, if you have two of the same 3-season sleeping bags that are individually rated to keep you warm down to 10 degrees. Then together these should keep you warm down to zero degrees because they have double the insulation. Having slept inside two sleeping bags I can tell you that it is incredibly nice and warm on a freezing cold night.
Adaptability
If your sleeping bag is designed to be used in arctic conditions then there is no way you can use that in the summer or you’ll cook yourself alive. Using two thinner or less insulated sleeping bags means that you can use them both all year round although maybe only one at a time in summer. Two sleeping bags can also be zipped together to make a double if you are camping with a partner.
Availability
Unless you are a camping enthusiast, gear addict, or equipment connoisseur, you most likely do not have a 4 season sleeping bag that is rated to work below zero degrees. There is a good chance though that you have access to a second sleeping bag that is either borrowed or a spare. In a pinch, you can also pick up a basic sleeping bag at many convenience stores and even gas stations. To get a sleeping bag that works in below zero degree conditions you really need a specialist retailer or to order online.
Cheap
Buying two average sleeping bags to make one super warm sleeping bag is actually significantly cheaper than buying one sleeping bag that is warm enough on its own. The other way in which you save money is that instead of owning two separate summer and winter sleeping bags, you just have one main sleeping bag and a spare. This spare can be lent to friends when you aren’t using it or kept in the car and so you have two sleeping bags that can be used year-round.
Comfort
Sleeping inside two sleeping bags adds double the thickness of padding between you and your sleeping pad. If you are on uneven ground this helps to cushion you from any hard lumps and get a better night’s sleep. This works better with synthetic sleeping bags as down-filled sleeping bags compress beneath you.
Problems With Doubling Up Sleeping Bags
While the benefits are fairly obvious, the downsides only become apparent once you actually try sleeping inside two sleeping bags at once. Here are some of the issues you may encounter:
Restrictive
Mummy-shaped sleeping bags are designed to be trimmed down sleek shapes that don’t have a lot of spare room inside. Just the fact that it tapers down to a very narrow footbox might be enough to put you off trying. The truth is that using a sleeping bag inside a sleeping bag setup is quite restrictive in that you feel quite squashed.
Rectangular sleeping bags are better suited to doubling up or at least using for the outer sleeping bag. Some sleeping bags have a small amount of stretch in their fabric which is also a plus when doubling up. At the end of the day, if you are not keen on feeling even more restricted inside your sleeping bag than normal then you probably won’t enjoy combining two.
Compress Insulation
The way a sleeping bag works is by providing dead space for warm air to get trapped both within the insulation itself and in the space between you and your sleeping bag. When you put a sleeping bag inside another sleeping bag you not only compress the insulation which prevents it from working very well, but you also lose the dead space inside your sleeping bag.
There is no avoiding the insulation beneath you compressing under your body weight but the effect is amplified when you do it with two sleeping bags. Synthetic insulation doesn’t rely so much on loft s down does and so is less affected but down is the preferred filling for premium sleeping bags.
Condensation
Some sleeping bags, especially down-filled sleeping bags, will have a DWR treatment on the outside of the shell fabric to protect the feathers inside. This DWR treatment is thin enough that condensation inside the sleeping bag can still escape but when you put another sleeping bag over the top of that it gets harder for the moisture to escape. Getting too hot inside two sleeping bags is a real issue but one that can be easily solved by opening the side zip like a vent.
Carry Two Sleeping Bags
A major downside to layering a sleeping bag inside a sleeping bag is that you have to carry two sleeping bags as opposed to just one winter sleeping bag. Synthetic sleeping bags are unavoidably bulky and the weight soon adds up. Down sleeping bags are much more lightweight but they also cost a small fortune. If carrying two sleeping bags is not an issue then there should be nothing stopping you from giving it a go.
What is the Best Sleeping Bag Combination?
The best combo, if you could choose, would be to use two down sleeping bags one inside the other. If weight isn’t an issue then a rectangular sleeping bag on the outside will have the least impact on restricting you inside your bag. If at all possible make sure that the side zips are on the same for both bags so that you can unzip them both for easy access inside your tent.
Conclusion
Is sleeping inside two sleeping bags a good idea and what is the best way to go about doing it? Putting a sleeping bag inside a sleeping bag is an easy way to double the warmth for cold weather camping without purchasing an expensive winter sleeping bag. The downside is you have to carry two sleeping bags and it can be a bit of a squeeze inside two mummy bags. Down offers the most forgiving compression and rectangular sleeping bags work best on the outside. Other than that, give it a go and let us know how it goes
