Gina Johnson
When the temperature drops, you might be tempted to combine two sleeping bags to keep warm. This method can work, but it's not always effective. The success of this approach depends on several factors, such as the type of sleeping bags used, the fit between them, and the environmental conditions. Using two sleeping bags can provide extra insulation, but it's important to consider the potential trade-offs, such as reduced breathability and increased weight. It's also essential to test the setup in a safe environment before relying on it in remote locations.
| Characteristics | Values |
|---|---|
| Advantages | Warmer than a single sleeping bag, no need to buy a new bag, fills in the voids that a single bag cannot |
| Disadvantages | Very difficult to know the exact warmth, may end up freezing or hot and sweaty, compression of insulation, weight, bulkiness, claustrophobia |
| Ideal Use Cases | Car camping with access to blankets and layers, testing in the backyard or cabin |
| Tips | Put the thinner bag inside, ensure the bags are not too tight, use a down bag inside for moisture control, test in single-night trips with an exit plan |
| Formula | Combined rating of two bags = Rating of Bag 1 + Rating of Bag 2 + 10°F |
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What You'll Learn
Combining two sleeping bags can make them warmer
Combining two sleeping bags can definitely make them warmer. Nesting one sleeping bag inside another can bump up the temperature rating. The warmth of a sleeping bag is determined by the amount of loft the fill provides. The more dead air a bag can trap, the warmer it will be. By doubling up on sleeping bags, you can increase the amount of dead air trapped and thus increase warmth.
However, it is difficult to know exactly how much warmer the bags will be once combined. This is because the insulation of the inner bag may be compressed, reducing its ability to trap heat. The rating will depend on compression and loft. The fit of the two bags is important, as if the inner bag is compressed by the outer bag, the insulation will not be as effective. It is generally recommended to put the thinner bag on the inside to maximise loft.
Some people have reported success with this method. One camper said that 15°F + 35°F bags kept him comfortable at 0°F, which is close to what a formula for calculating the warmth of two bags predicts. Another person reported being comfortable at -18°C using two 0°C bags. However, it is important to test the setup beforehand, as some people have reported being cold using two bags.
There are a few drawbacks to this method. Firstly, the weight of two bags may be more than you want to carry. Secondly, it can be claustrophobic if the bags are the same size. Finally, it may be safer to have one bag rated for extremely cold temperatures rather than relying on two bags, especially if you are backpacking in the middle of nowhere.
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The thinner bag should go inside
Nesting two sleeping bags can theoretically keep you warmer than a single sleeping bag. However, it is challenging to determine the exact warmth level of the combined sleeping bags. Many factors, including the quality of fill, construction, and loft, influence the warmth of a sleeping bag. When using two sleeping bags, it is generally recommended to place the thinner bag inside the thicker one. This configuration maximises loft, as compression can reduce the insulation and warmth of the inner bag.
The warmth of a sleeping bag depends on the amount of loft, or fluffiness, it provides. A good down bag designed for temperatures of 20°F will typically have 4–5" of loft. By nesting two such bags, you could theoretically achieve 8–10" of loft, which would provide more warmth. However, if the bags are too tight, the inner bag may become compressed, reducing its loft and overall warmth.
To optimise warmth, it is crucial to consider the fit of the bags. Ensure that the inner bag has sufficient space to loft properly without being compressed by the outer bag. Additionally, pay attention to the zippers. If possible, align the side zips of both bags for convenient access.
When combining a down sleeping bag with a synthetic bag, it is generally recommended to place the down bag inside. This arrangement helps with moisture control. Your body produces water vapour, which will travel outwards until it reaches a temperature where it condenses into water. By placing the down bag inside, you prevent condensation from forming within the down material, as synthetic bags can better withstand moisture.
While nesting two sleeping bags can provide additional warmth, it is important to consider the potential drawbacks. Combining bags can result in breathability issues, leading to a stuffy and sweaty experience. Additionally, carrying two sleeping bags can be bulkier and heavier than a single winter bag. Therefore, it is advisable to test the setup in a controlled environment before relying solely on this method in extreme conditions.
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Loft (fluffiness) is key to warmth
When it comes to staying warm, the loft, or fluffiness, of a sleeping bag is crucial. The basic warmth of a sleeping bag is determined by the loft of the fill—the more loft, the warmer the bag. Quality of fill also impacts how much loft is necessary for a given level of warmth. A good down bag designed for temperatures of 20°F will typically have 4–5 inches of loft.
Using two sleeping bags can theoretically provide more loft and, therefore, more warmth. However, this depends on several factors. Firstly, the bags should not constrict each other, as this can reduce loft and compromise warmth. The inner bag should have enough space to maintain its loft without being compressed by the outer bag. The bags should also be layered so that the thinner bag is on the inside, as compression of the inner bag's insulation will reduce its ability to trap heat.
The type of sleeping bag is also important. Down bags generally provide better moisture control than synthetic bags, as they handle sweat moisture better. However, if condensation forms in the tent, it is preferable for it to drip onto a synthetic bag rather than a down bag. When using a down and synthetic bag together, the down bag should be on the inside, with the synthetic bag providing protection from condensation.
While using two sleeping bags can provide extra warmth, it may also lead to breathability issues. The combination of two bags can result in a hot and stuffy environment, trapping sweat and leading to evaporative heat loss. This can be mitigated by draping the second bag over the first or unzipping it and nesting only the foot area.
In conclusion, when considering using two sleeping bags for added warmth, it is essential to focus on maximising loft. The bags should be combined in a way that avoids compression and allows for adequate breathability.
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It's hard to know the exact warmth of two bags combined
It is challenging to determine the exact warmth provided by combining two sleeping bags. Sleeping bag liners, clothing, and the number of people using the bags can all affect the temperature. For instance, a camper reported that a 15°F + 35°F bag combination kept them comfortable at 0°F, while another camper with a 15°F + 40°F bag setup claimed to be comfortable at the same temperature.
The warmth of a single bag depends on the amount of loft the fill provides, which is influenced by the quality of fill and construction. A good 20°F down bag, for instance, should have 4-5" of loft. Theoretically, combining two such bags would provide 8-10" of loft, resulting in a temperature rating of around *-10°F or lower. However, in reality, the inner bag may be compressed, reducing its effectiveness and resulting in a higher temperature rating of around *-5°F.
The type of sleeping bag also matters. For example, a down sleeping bag should be placed inside a synthetic bag to manage moisture better. Additionally, the bag with the slimmest profile should be used as the inner bag to maximise loft.
It is recommended to test the warmth of the combined sleeping bags in a controlled environment, such as a backyard or cabin, before relying on them in extreme conditions. This will help determine if the combination provides sufficient warmth and breathability.
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Test your setup before relying on it
It is important to test your sleeping bag setup before relying on it in the wild. While using two sleeping bags can definitely make you warmer, it is hard to know exactly how much warmer you will be. There are many variables to consider, such as your body, loft, compression, and vapor. Even a formula that considers the temperature ratings of the individual bags is not always accurate.
The best way to test your setup is to try it out in your backyard for a single overnight. This way, if it doesn't work, you can easily go inside. You can also try renting a cabin and camping in front of it, so you have a backup plan if you get too cold. It is important not to test the two-bag system on multi-night trips until you know it works for you.
When testing your setup, make sure to eat a big meal beforehand. This will help you stay warm. You can also try draping the second sleeping bag over the first or unzipping it almost all the way and only nesting the foot area. This setup creates large air gaps but maintains breathability. If you are using a down and a synthetic bag together, put the down bag inside, as this setup is better for moisture control. You can also try using a liner to add warmth.
It is important to consider the fit of the two bags and whether one compresses the other. If the inner bag is compressed, it may not insulate properly. To avoid this, choose bags with girths that do not compress each other. Additionally, the thinner bag should be placed inside, as it will have more loft (fluffiness) this way. You can measure the loft of different setups to determine which will be the warmest.
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Frequently asked questions
Yes, using two sleeping bags will definitely be warmer than using just one. However, it is difficult to know exactly how much warmer it will be, and you could end up either too hot or still too cold.
The thinner bag should go on the inside, as insulation doesn't trap heat well when compressed. The outer bag should be large enough for the inner bag to loft properly.
The exact temperature rating of two sleeping bags is difficult to determine. It depends on factors such as the quality of the fill, construction, and loft. A formula floating around backpacking forums suggests that the warmth of two sleeping bags can be calculated by adding the temperature ratings of each bag and then subtracting 20F. However, this formula has been disputed.
It is recommended to test out using two sleeping bags in a low-risk setting, such as in your backyard or by renting a cabin and camping in front of it. This way, if the two-bag system fails, you can easily retreat inside.
