Never underestimate the power of a good night’s sleep! Refreshing. Rejuvenating. And when out on the trail…
100% necessary for your survival.
That’s why we need to talk about how to stay warm in your sleeping bag. Because if you’re getting ready for an expedition of epic proportions, you NEED to know how to make your sleeping bag warm (and keep it that way!). It’s better than freezing to death anyway.
There are two parts to getting a good night’s sleep in a sleeping bag:
- Investing in the right bag for both your build and style.
- And knowing exactly how to use it.
So that’s exactly what we’re unpacking here—how you can find the right bag for your build and your adventure style. And then, how you can heat that sleeping bag so not even subzero temperatures can ruin your rest!
Ready for some epic education? Good!
Because in the battle against cold, every degree counts
How Sleeping Bags Lose Heat
Learning how to make a sleeping bag warmer is as much about science as it is about buying premium gear. There’s no sense in having a top-shelf, over-9000-down 0-degree bag if you don’t know how to keep it warm throughout the night.
Primarily, there are four processes that cause heat loss:
- Conduction
- Convection
- Radiation
- Evaporation
Each plays a key role in both heating a sleeping bag and its subsequent heat loss. So, by understanding these processes, we can effectively apply techniques that help us stay warm in our sleeping bags on those wild and wintry treks.
Conduction occurs when your body’s heat transfers to the cold ground beneath. A cold hard ground is one of the biggest killers of a good night’s sleep outdoors. Without proper insulation beneath us (like a well-designed sleeping pad), body heat rapidly escapes into the earth, leaving you with an inescapable chill.
Meanwhile, instead of beneath you, convection is what happens inside your sleeping bag. If there’s too much space inside your bag, cold air circulates through and siphons off warmth. To avoid this, the top priority is simply picking the right bag. A bag that’s too large or doesn’t cinch around the head right is a one-way ticket to convection county!
Radiation is your body’s natural heat emission. Even mid-tier sleeping bags will be constructed from materials that trap body heat effectively and reflect it back at you. However, the better the bag you buy, the better designed the insulation will be.
Finally, evaporation. Evaporation happens when moisture, such as sweat or condensation, cools you down as it evaporates from your skin. It’s important to know how to stay warm in a sleeping bag… But you also don’t want to stay so warm that you sweat or condense up the bag.
Some Ways to Stay Warm in a Sleeping Bag
These are the four atmospheric reactions that define the awesomeness of your pitch. Together, these four factors are why simply having a top-of-the-line sleeping bag isn’t enough.
To survive cold nights sleeping below freezing in a bag, you need a strategy. It’s your sleeping bag plus every tool in your adventure-ready utility belt that keeps you warm at night.
So, no more theory! Do you want to know exactly how to stay warm in a sleeping bag? Here are 10 tips for sleeping soundly, no matter whether it’s a brisk night by the lake or the dizzying heights of K2 Base Camp!
Store Your Sleeping Bag Properly
Improper sleeping bag storage leads to improper insulation. Both down and synthetic insulation rely on its “loft” to trap heat (i.e., its floofiness factor). The floofier your bag is, the warmer it is.
Long-term compression and storing a bag in a compressed state degrades its loft. Down bags are especially vulnerable to this, and while synthetic insulation is better equipped for compression, it’s still far from good.
The bottom line is don’t squash your sack! When you’re not using your sleeping bag, store it loose in a mesh or cotton bag—hanging it up somewhere is even better. And no matter what, air out your bag and dry out ALL dampness before storing it.
Better storage means a better bag for many years to come.
Use an Insulated Sleeping Pad
Combat conduction! As mentioned, a good sleeping bag is crucial. Arguably, having the right sleeping pad is even more crucial for staying warm at night than your sleeping bag.
Your first step is to examine the pad’s R-value. The R-value directly measures a pad’s resistance to heat loss. The higher the R-value, the better the insulation.
For cold-weather camping, it’s best to invest in a pad with an R-value of 4 or higher. In terms of the type of sleeping pad, closed-cell foam pads or insulated inflatable pads are both top-tier choices.
If you already have a pad, but it’s still running cold, you can also employ a few quick tricks:
- Layering two sleeping pads instead.
- Place a yoga mat or foam pad beneath your primary pad.
- Or even a cardboard barrier between the pad and the ground.
Basically, any extra protection between you and the ground is key to staying warm in a sleeping bag. But best-case scenario: just get yourself the sleeping pad you deserve.
Sleep with Warm Items
As for how to make your sleeping bag warm inside… Fill it with warm things!
For example, you can try:
- Putting a hot water bottle in your sleeping bag.
- Or a Nalgene or metal bottle filled with hot water.
- Heating rocks by the fire.
- Or even using hand warmers inside a sleeping bag.
Adding heat directly inside your bag works wonders. A hot water bottle is the gold standard, and the rest are just classic hiker’s tricks for ounce-counters who don’t want to pack one!
(Plus, you can also pre-warm your sleeping bag by placing a warm bottle or hot water bottle inside for 15-20 minutes before you get in.)
Have the Proper Clothing On
Snug as a bug vs overheating and sweating: finding the right balance to get a good night’s sleep is a tricky game!
Let’s take it in layers:
- Base Layer: Start with a moisture-wicking base layer, such as merino wool or synthetic fabric, that keeps sweat off your skin.
- Mid-Layer: Fleece or something similar (i.e., flexible, warm, and comfy) is perfect.
- Top-Layer: On seriously cold nights, a light down jacket can tie your evening fit together. However, save it for very cold nights to avoid sweating.
- Extremities: Protecting your extremities is often even more impactful than a top layer! Wool socks, a beanie, and even using a hiking buff or balaclava for extra face warmth are great additions to your layering system.
Just ensure you avoid overdressing! Too many layers actually compress the insulation inside your bag, making it less effective, and obstructs radiation from your body, which in turn heats the bag.
So layer smartly, stay flexible, and don’t sweat the small stuff.
Pro tip: make sure that when you’re dressing to sleep, your layers are even. For example, wearing too much on your upper body and too little on your lower body creates uneven radiation and, consequently, a less toasty sleeping bag.
Make Sure You’re Going to the Bathroom
There’s a lot of fun science to this one! Your body uses energy to keep the urine inside a full bladder warm—energy that could be heating you and your sleeping bag instead.
Not peeing before bed is a direct net loss of sleeping warmth. Moreover, getting up halfway through the night for a moonlight leak is NOT fun. (Though often very beautiful!)
If leaving the tent feels unbearable, keep a clearly labeled pee bottle on hand. Alternatively, women can use portable urination devices (like the She-Wee) for convenience.
They’re certainly not glamorous solutions. But honestly, something like the She-Wee is an essential item for lady trekkers regardless of cold nights. Staying warm and dry is always worth it… and sometimes life just calls for a pee bottle.
Add Extra Insulation
A sleeping bag warmer or liner is a camper’s best friend for added warmth. We kind of like to think of them as a bedsheet for your bag.
Thermal or fleece liners alone boost your sleeping bag’s temperature rating by up to 10–20°F. They’re also easy to wash and serve as a protective barrier between your stinky hiker feet and your bag’s interior. You can make your sleeping bag warmer and keep it around for longer.
Alternatively, try layering a big quilt or blanket over your bag for an extra buffer against cold air. You could even layer your bag with a bivy sack to block wind and trap more heat on very cold nights…
Basically, when in doubt, take more blankets!
Don’t Overheat
Over-layering is one cause of overheating, but it’s an easy fix. More broadly, general overheating and a lack of bag ventilation and airflow are what really get you.
If you’ve nailed in your sleep system and are sleeping sound, then your body temperature will rise overnight inside your cocoon. Body temperature rises, sweat occurs, there’s more moisture coming from your breath and skin… And when all that moisture and dampness evaporates, you get cold.
Staying warm in a sleeping bag is often also about not getting too warm. Look out for the signs of overheating:
- Feeling clammy or stuffy
- Needing to unzip frequently
- Lightly sweating
- Waking up damp inside your bag.
Then, prevent overheating with the appropriate temperature management:
- Ventilate Well: Use your sleeping bag’s two-way zipper wisely. Unzip it to let out excess heat, however, try going a quarter of the way down or even halfway up from the bottom to avoid fully opening the bag.
- Start Light on Layers: Start with light layers, even if you’re feeling a bit cold at first. Chances are you’ll warm up as the night goes on, and you can always add more layers later if necessary.
- Loosen Your Hood: Overtightening it traps heat and moisture around your face. Also, try leaving your face exposed and not inside the bag to prevent condensation buildup from your breath.
Eat a Good Meal
Here’s a fun tip for staying warm in a sleeping bag because it means you get to eat more! Eating a meal before bed helps you stay warm at night in a sleeping bag.
When you sleep, your body operates like a furnace. It breaks down and burns all the fuel inside in exchange for a pleasant organic central heating system. But that also means your body needs fuel.
So what’s the ideal fuel? A hearty meal rich in protein and fats. Something along those lines, like a chili dish, stew, or even most ready freeze-dried meals, is ideal. These hiker-friendly meals have macronutrients that digest slowly, providing sustained warmth throughout the night.
Otherwise, in a pinch, you can try some pre-bed snacks for a quick bit of warmth:
- Nut butter wraps or trail mix: Packed with protein, fats, calories, and plenty of snackability, trail mix is one of the best outdoor snacks around!
- Cheese and crackers: Slow-digesting and satisfying. It’s not the most nutrient-dense option, but it warms you up.
- Chocolate or an energy bar: If you need a quick pick-up, these work great.
- A spoonful of cooking oil: E.g. olive oil. This is less of a delicious snack and more of an old hiker’s hack you learn when starting out mountaineering.
Lastly, hot drinks help raise your core temperature. BUT don’t overdo the pre-bed tea. A 3 AM bathroom trip quickly nullifies the degrees you gained from the snacks.
Share with Your Partner
Sharing a tent with another human already ups the insulation factor. But sharing a bag is both cozy and cuddly.
Lean into your shared natural body heat to make a sleeping bag warm at night. For couples, kids, and best mountaineering bros, look for sleeping bags designed to zip together. This gives you versatility between both single sleeping setups and sharing. Alternatively, double-wide sleeping bags are another good option.
Even without a shared bag, cuddling under a shared thermal or emergency blanket can help a lot. Or, if you enjoy adventuring with a furry friend, bring your doggo inside your sleeping bag. You’ll be warmer, and your pooch will be the snuggest of bugs in a rug.
Stuff the Bottom
The foot of your sleeping bag is a notorious cold spot. All that empty room is just dead space and extra air your body has to heat.
To get around this, fill the foot box with soft, insulating items like your down jacket or extra clothes. If your clothes are damp, you can even stuff them inside your bag to begin drying them for the next morning’s hike by using your body heat.
However, treat this tip as an emergency winter survival trick. Only lightly damp woolens and synthetics should be stuffed in your bag—but never soaked gear and never down.
Choosing the Right Sleeping Bag in the First Place
Right, that’s a lot of expert tips on how to stay warm in a sleeping bag. Nevertheless, it still all starts with your choice of bag.
So, to help you on your way, the A-class adventure team at Epic Expedition has got some grade-A selections for you!
We really can’t stress how important it is to NOT skimp on your bag. You can go more budget-friendly with some elements of your hiking gear; however, a sleeping bag (and pad) is your lifeline in cold climates and is not to be skimped on.
Marmot Never Summer - The Most Budget-Friendly 0-Degree Bag
If you’re truly on a limited budget, the Marmot Never Summer is a great bang for your buck. Designed for harsh, sub-freezing temperatures, this zero-degree sleeping bag is built for winter expeditions with its 650-fill-power-down insulation. Combine that with a Down-Defender water-resistant treatment and an insulated draft tube and hood to lock in warmth, and you have yourself a truly supreme bag for a good price.
REI Magma - The Best All-Around Sleeping Bag for Subzero Temps
Option two is a more general recommendation for the broader market: the REI Magma—a top-rated star from REI’s own in-house gear lineup. The Magma is renowned for its superior warmth on an ultralight weight-budget, using premium 850-fill goose down to keep weight low and comfort high.
But what really makes this bag shine is the variety of sizing and fit options available. With cuts and lengths available for every shape and size of human, you can choose a version that fits your body perfectly. That means no dead air footbox or improperly fitted hood! If you weren’t finding the fit of the Never Summer right, this is a very competitive and customizable counterpart.
Nemo Disco 15 and Riff 15 - The Best 4-Season Bag for Side Sleepers
Lastly, we have the Nemo Disco 15 and Riff 15—a personal passion pick for side sleepers. Speaking for many side sleepers, finding a comfy and well-insulated bag fit for those rolly-polly nights can be a serious challenge. Then along comes Nemo’s signature spoon-shaped sleeping bag design.
This innovative little twist on the classic offers extra room around the knees and elbows, making them a dream for restless or side sleepers. In essence, they’re very similar bags; the Disco sits at the more mid-range level, although it still provides excellent warmth with hydrophobic down insulation. Conversely, the Riff 15 is the more premium choice, offering a trimmer cut and additional down filling—ideal for ultralight hikers.
Both come in men’s and women’s cuts, which you can find linked below:
Wrapping Up: Start Making Your Sleeping Bag Warmer
Overall, to summarize, don’t cheap out on a sleeping bag. A good night’s sleep out in the wilderness is one of the best things about hiking. And the better you sleep, the more you actually enjoy the hike.
It’s about safety. It’s about pleasure. It’s about being wise in the wilds.
And if nothing else, just remember, it never hurts to have a cuddle buddy. 😉
