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 below freezing. Countless frosty nights sleeping outside over the past three-plus decades 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 cold you normally sleep outside, or whether you’re camping in the backcountry or at a campground, these 10 tips will keep you warmer in your sleeping bag.
#1 Clean Up
At the end of each hiking day, wash the dried sweat from your body; it can act like a heat conductor, chilling you. I swim in a lake or creek when possible, or wet a bandanna or other cloth to wipe myself off.
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#2 Change Into Dry Clothes
Change into dry clothing to sleep, as opposed to the clothes you sweated in while hiking; damp clothes promote conductive heat loss from the body.
#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 layers (think: one or two base layers, or a base layer and a light insulation piece) on your body and line your bag with other extra clothing, which provides added insulation for your entire body.
#4 Use a Hot-Water Bottle
Stick a water bottle (like a plastic Nalgene bottle, not an insulated or vacuum bottle, which would not release any heat) 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.)
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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
Pile extra clothing under the foot end of your bag to give your feet more insulation against the cold ground.
#8 Use a Bag Liner
Use a sleeping bag liner, which can add the equivalent of several degrees of warmth rating to a bag.
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#9 Eat Some 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.