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I've got a sleeping bag, rated at 15°c comfort, 6° limit and -8° extreme. I'm planning on a backpacking trip bivvying with a tarp. Currently the nighttime temperature is about 2-4°c. Is there any way to cheaply and easily increase the range of the bag with minimum extra space or weight? Or will this be a suitable set up as is?

(I could possibly use a cotton liner)

  • 1
    This will be bearable, but pretty un-fun even with a liner. – Joe Manlove Mar 24 '15 at 0:35
  • You could just wear a lot of clothes to bed, including thick wool long underwear and a wool cap. – Ben Crowell Mar 24 '15 at 15:58
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Using a sleeping bag liner can usually add 5-8°c or more warmth capability to your sleeping bag.

However, do not use a cotton liner if you are in cold climates, as that can hold onto moisture from your body and cause you trouble.

  • 2
    Yes, don't use a cotton one. A silk one would be ideal – user2766 Mar 24 '15 at 8:36
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    @Liam - A silk bag liner is not the cheap solution to increasing the temperature range of your bag. A silk liner can cost almost as much as a new synthetic bag rated to 0°C. A cotton liner costs less than half as much as silk, and keeps you about as warm. I use my cotton bag liner for winter camping, I find it super comfortable sleeping in my -10°C bag at -15°C to -20°C, and all I wear inside it is a polyester base layer. – ShemSeger Mar 24 '15 at 16:01
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    They're not that much if you shop about, here's a rab one for £26! – user2766 Mar 24 '15 at 16:25
  • @Liam, that is a much more reasonable price, but it appears to be a thinner silk (I'm guessing by it being 50g lighter), so probably not as warm. Still, at £40 retail, it's almost half the cost of the one I linked. – ShemSeger Mar 24 '15 at 21:47
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I've used a cotton bag liner for winter camping for the past couple years, I love it. I'm usually a huge opponent to wearing cotton in winter, but that's because most people are pretty careless about moisture control these days. If you read my answer to, "Does Cotton Really Kill?", I point out that cotton was worn on the very first summit of Everest.

The important thing is to be dry when you get into bed and properly layer your bag. See my answer to this question about layering in your sleep. I think you're fine with cotton liners as long as you don't over-layer inside your bag. Too many clothes layers will make you feel clammy in your bag, but fewer layers means your bag can get warmer, and having a warmer bag means the moisture inside it is more likely to vaporize and breath out of the bag.

Although it may seem like thin bag liners may add temperature to the bags (and I'm one of the one's who's convinced that they do) they technically aren't designed to make your bag warmer, they're designed to keep it cleaner and more comfortable, a fleece liner would add the most warmth, and it also happens to be the cheapest option compared to silk and cotton. The advantage to silk is that it's by far the lightest and most compact option, but costs almost as much as a new affordable sleeping bag.

One thing that will keep you significantly warmer while sleeping on the ground, is to use a reflective ground sheet, like an emergency blanket, or a nice insulated air mattress. You lose a lot of warmth into the ground due to conduction, so it's important to put something between you and the cold Earth.

Other ways to keep warm at night include eating a lot of calories just before bed (stoking the oven) and making sure you pee before crawling into your sleeping bag, as extra water takes extra energy to keep warm.

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In my experience the two most important things you can do to improve the range of a bag are:

  1. Improve your ground insulation.
  2. Warm your extremities.

Ground insulation is far more important than most people appreciate. If budget is no object you can invest in the NeoAir Xtherm, which is a breakthrough product. On a tight budget you can buy closed cell foam mats. Take along as much as you can carry. You can also insulate the ground under your bag with natural materials such as heather or dry leaves.

Warming your extremities also makes a big difference. What you need are warm, dry sleeping socks, gloves and hats. A scarf or buff around the neck works well too.

Good luck!

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