How to Stay Warm in a Sleeping Bag

Whether you’ve just plunked down your hard-earned dollars on a brand new sleeping bag, or you’re still using a trusty old bag that’s seen better days, you can help ensure you’ll be warm and cozy on your next outdoor adventure with a few simple tips.

To stay warm in your sleeping bag, follow three main strategies:

  1. Defend against the major sources of heat loss: A bag liner, an insulating pad, a tent and a well-chosen campsite can help reduce the heat-sapping effects of radiation, conduction and convection, and help you preserve body heat as you sleep.
  2. Avoid sneaky types of heat loss: Wearing dry clothes, covering your head and emptying your bladder before you sleep are simple tricks for maintaining warmth.
  3. Add heat from other sources: High-carb snacks, light exercise and sharing body heat all help to keep your interior furnace stoked.

Let’s look at the strategies in a little more depth. 

Major Types of Heat Loss

  • Radiation: Your body emits heat and your sleeping bag’s primary mission is to contain that heat for you. One way to give it a boost, though, is to add a sleeping bag liner. A liner can add from 5 degrees to 15 degrees of warmth to your bag and, as an added perk, it helps keep your bag cleaner.
  • Conduction: When your body contacts the Earth, you open up a conduit for heat loss. And the planet is a lot bigger than you are, so it can suck up all the heat your body can produce. So, you should always have an efficiently insulated sleeping pad between you and the cold, hard ground.
  • Convection: Cold air around your body also whisks away heat. So, sleeping in an enclosed area—your tent—keeps warmth from escaping into the night. It also protects against rapid heat loss by blocking breezes to prevent windchill. Picking a tent site that has a natural windbreak, like a healthy stand of trees, also helps.

Other Heat-Stealing Scenarios

Heat can disappear in less-obvious ways, so you should also consider the following cold-prevention tactics:

  • Sweaty clothes: Moisture evaporates and siphons off heat, so always sleep in dry clothes. Using a pair of wool or synthetic long undies for sleepwear is always a solid choice.
  • A bare noggin: While it’s not true that you lose an outsized amount of heat through your head, you do lose heat through any exposed body part. So, if your bag has a mummy hood, use it. If not, slip on a beanie when you don your sleeping togs.
  • A bloated bladder: Your body has to keep everything at the same temp, which means it uses up heat to warm your pee. Manage your drinking to minimize what’s in the pipeline, then empty your bladder at bedtime. And if Nature still calls in the wee hours, it’s best to answer.

Adding Heat from Other Sources

Most warmth tactics involve retaining the limited amount of heat your body can produce. You can also give it a hand with a few of these tricks:

  • Fuel up: Eat a snack before bed; complex carbohydrates—energy bars (or other foods) with whole grains—are ideal because they provide a steady supply of energy that’s released over time as your body slowly digests them.
  • Cuddle up: It turns out that spooning is good for you both emotionally and physiologically. So if you camp with the one you love and you have bags that zip together or a couple-size bag, then share the warmth.
  • Limber up: Some light exercise right before bed, maybe a few sit-ups, can help your body produce a little energy for the night. The trick is to do enough to get warmed up, but not so much that you break a sweat.

Following the strategies here will help you enjoy a greater level of warmth in any sleeping bag.  They won’t make up for a bag that’s woefully under-insulated for the conditions of your trip, though. If it’s time to get a new sleeping bag, we can help. For advice about choosing the right bag, check out How to Choose Sleeping Bags for Backpacking and How to Choose Sleeping Bags for Camping.

Be Wary of Overheating   

Cold sleepers sometimes think there’s no such thing as too much heat. If you overdo these tactics, though, you can break a sweat in the middle of the night. That can lead to evaporation and feeling cold again. So be like Goldilocks: not too cold and not too hot.