How Does a Sleeping Bag Keep You Warm?

By Charles •  4 min read

When camping, you need a suitable sleeping bag to keep warm and avoid frigid nights. But just how does a sleeping bag keep you warm? And how can you ensure that you get the maximum value out of your bag? The following information will help you understand why your sleeping bag is warm and how to keep it that way.

How Does a Sleeping Bag Keep You Warm

So, just how does a sleeping bag keep you warm? They work like other blankets but have the advantage of covering all of your body, whereas a blanket only covers the top half. All sleeping bags and blankets are filled with insulation, both natural and artificial, that traps heat and holds it.

And your sleeping bag traps your body heat as it leaves your body, allowing the bag to warm up trapped air and hold this heat as close to your body as possible. As a result, you get extra warmth on all sides of your body. And as the sleeping bag only has one heat exit (the opening where your head rests) it doesn’t lose nearly as much heat as a traditional blanket.

How are Sleeping Bags Insulated

Sleeping bags typically consist of either natural goose down or synthetic insulation. Goose down consists of goose plumage stuffed inside the sleeping bag. This insulation is sewed into the sleeping bag’s interior layers and spread out evenly to produce a very warm level of insulation. Higher “fill” numbers indicate a higher overall warmth, with 900 and above being useful for sub-zero camping.

Synthetic insulation is created in a laboratory and consists of materials designed for maximum insulation strength. Though they produce a similar heat level to that of goose down, they do not pack or roll up nearly as quickly. As a result, it is essential to consider whether this option is right for you to avoid making an unfortunate purchasing mistake.

How to Stay Warmer in a Sleeping Bag

How does a sleeping bag keep you warm and how can you get it warmer? Ensure that you close up the top of your sleeping bag as much as possible to minimize heat loss as you sleep. You should always put a sleeping pad down, as well, because the bare ground will rob you of much heat and cause a lot of shivering as you try to rest at night.

Always wear dry clothes as you sleep, as sweaty or wet clothes may decrease your temperature. Just as importantly, make sure to keep as much of your body in the bag as possible to avoid lost heat. You may even want to wear socks and gloves to prevent lost heat through your extremities.

Pro-tip: a good thermal hat will prevent a lot of body heat loss while you sleep.

How To Increase Sleeping Bag Warmth

Wear Warm Clothes While In Your Sleeping Bag

Extra layers of clothes can help here, but there comes a point when putting on more clothes doesn’t make your sleeping bag warmer. That’s because you may press too much against the insulation and limit its ability to absorb and hold heat.

Sleeping Naked Does Not Necessarily Keep You Warmer

Whoever started this myth did a good job of spreading it because it pops up in just about every amateur camping blog. The explanations for this idea always use shaky scientific ideas, usually stating that nudity helps the warmth of the sleeping bag transfer to your body more quickly, preventing heat loss and keeping you warmer.

But that’s not how thermal transfers work, and you’ll be colder naked in a sleeping bag. Your clothes operate on the same thermal principles as your sleeping bag, trapping warmth against your body and preventing thermal transfer. So if you’re cold in your sleeping bag, don’t take off your clothes – instead, you can try a sleep liner or add on another layer of clothing, if possible.

Use Sleeping Bag Liners To Help Keep You Warm

You may be on the fence about a sleeping bag liner but a high-quality liner can provide a surprising amount of extra warmth, depending on the material you utilize. If you want the warmest possible bag for winter camping you need to get thermal synthetic, microfiber, micro fleece, or merino wool liners. These can add up to 10-25 degrees Fahrenheit to your sleeping bag. If you just want a comfortable but not too hot bag, such as for spring or early summer camping, a silk or cotton liner should be more than enough extra warmth for your needs.


Charles is a man who loves the outdoors. He moved to Wyoming specifically to spend more time in the mountains and wilderness. A hunter and fisherman, Charles knows how to enjoy nature and all that it has to offer. He is an outdoorsman through and through, and he wouldn't have it any other way. Charles is the President of Absaroka Enterprises, an company focuse on outdoor entertainment and endeavours. He's also an Editor for Alpha and Omega Outdoors, an online hunting, fishing, camping, trapping, and all around outdoors blog.

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