By Michael Lanza
Head into the mountains in summer, or almost anywhere in fall or spring, and you can encounter nighttime and morning temperatures anywhere from the 40s Fahrenheit to well below freezing. That’s more than cold enough to pose a real risk of hypothermia or, at the least, result in a miserable night for you or a partner or child you’ve taken backpacking or camping—and would like to take more. Here’s the good news: The very simple techniques outlined in this article can turn a potentially unpleasant night into a comfortable one.
Countless frosty nights sleeping outside over the past three-plus decade—including the 10 years I spent as a field editor for Backpacker magazine and even longer running this blog—have taught me a few things about how to stay warm. (My coldest night was -30° F, in winter in New Hampshire’s White Mountains. I don’t recommend it.)
No matter how easily you get cold when sleeping outside, or whether you’re camping in the backcountry or at a campground, these 10 tips will keep you warmer on cool and chilly nights in your sleeping bag.
Tell me what you think of my tips, ask any questions, or share your own tips in the comments section at the bottom of this story. I try to respond to all comments.
1. Clean Up
At the end of each hiking day, wash the dirt and dried sweat from your body; the latter can act like a heat conductor, chilling you, and getting a bit cleaner will just make you feel better. Swim in a lake, wade into creek and splash water all over yourself, or at least wet a bandanna or other cloth (or use wet wipes or other such products) and wipe yourself off.
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2. Change Into Dry Clothes
Damp clothes promote conductive heat loss from the body. Change into dry clothing to sleep, as opposed to the clothes you sweated in while hiking.
3. Dress Smartly
Inside your bag, wear a hat, socks, and extra layers on your body, but avoid putting on so many layers that you isolate your core, which is your body’s furnace, from your extremities, which get cold more easily. It’s often more effective to wear just one or two light to midweight base layers—that are highly breathable, so as to allow your core’s heat to disperse throughout the bag. If you need more warmth, lay an insulation piece over your torso and hips inside the bag, essentially boosting the bag’s insulation, and stuff other extra clothing around you or at the foot of your bag to provide added insulation for your entire body.
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4. Use a Hot-Water Bottle
Stick a water bottle filled with hot water in the foot of your bag. If that’s not enough, put a second bottle filled with hot water in the middle of your bag. Make sure they’re sealed tightly and that you’re using a sturdy, plastic bottle that’s designed to hold hot liquids, like a Nalgene bottle; a cheap plastic bottle (like an empty soda bottle) could split open, a potentially very dangerous situation. An insulated or vacuum bottle would not release any heat, negating any benefit.
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5. Sleep on Insulation
Use an insulated pad or air mattress rated for the lowest temperatures you expect to encounter. Mats and pads with an R-value of between 3 and 4 are intended for three-season temperatures—generally, above freezing—while those with an R-value of over 5 are intended for use on frozen ground in below-freezing temperatures. If needed, add a second foam pad under your primary air mat if you’re sleeping atop frozen ground or snow.
6. Augment Your Sleeping Pad
If you’re using a short air mattress or foam pad (to save weight in milder temperatures), lay your empty pack beneath your feet to insulate them from the ground, which can drain heat from your body even in summer. Or bring a short foam pad to provide more padding and insulation under a full-length air mat.
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7. Pile Extra Clothing Underfoot
Your feet get cold more easily than other body parts because they lie the farthest from your heart and, inside a sleeping bag, are not close to your furnace: your body’s core. They can also get cold because the ground under your sleeping pad is cold. Pile extra clothing under the foot end of your bag to give your feet more insulation against the cold ground.
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See my “5 Tips For Staying Warm and Dry While Hiking.”
8. Use a Bag Liner
Use a sleeping bag liner, which can add the equivalent of several degrees of warmth rating to a bag.
9. Eat Fat and Sugar (The Fun Tip)
Eat a snack high in fat right before bed, like a candy bar, and have a hot drink with sugar in it, like hot cocoa. Both will fuel your body’s furnace through the night.
10. Use Your Partner
If you’re sharing a tent with a partner who doesn’t get cold as easily as you, ask that person to sleep on the tent’s windward side. If you have two warm-sleeping partners, sleep between them, or at least position your bags and pads close together to benefit from one another’s body heat.
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Whether you’re a beginner or seasoned backpacker, you’ll learn new tricks for making all of your trips go better in my “12 Expert Tips for Planning a Wilderness Backpacking Trip” and “A Practical Guide to Lightweight and Ultralight Backpacking.” If you don’t have a paid subscription to The Big Outside, you can read part of both stories for free, or download the e-guide versions of “12 Expert Tips for Planning a Wilderness Backpacking Trip” and the lightweight backpacking guide without having a paid membership.