Winter adds a whole new set of risks and challenges for backcountry campers and hikers to manage. Heading out into icy cold, howling winds and deep snow can be scary for someone who isn’t used to living and surviving in that sort of environment without the creature comforts of home.

That’s why I put together this guide that lays out all of the essential winter survival tips for hikers and backpackers – and the science to back it up. If you’re thinking about heading into the outdoors this winter, make sure you know everything in this article.

I broke it up into a few key sections for better navigation:

Dressing for Warmth & Comfort

When it comes to being warm and comfortable in the winter, always think about layers. Wearing multiple, light layers allows you to customize your level of insulation as your needs change throughout the day.

Somewhat counter-intuitively, the main thing you want to think about is avoiding overheating – once you start sweating you’ll have moisture between your layers which can freeze and generally drain your body heat much faster than if you stay dry.

I talk more about layers in my article on Winter School, but the general principles are as follows:

Base Layer - A thin layer that pulls moisture away from the skin as your sweat. Wool is a great natural base layer, and there are many synthetic materials that also serve well. Absolutely no cotton – that includes most denim, khaki and flannel – once it’s wet it makes you colder than if you were naked (see above graph). Insulating Layer - The insulating layer traps a pocket of warm air around you to act as a barrier against the cold. Insulation could be fleece or wool, or something puffier like a synthetic- or down-filled layer. Shell - A “hard” outer layer that protects you from wind and precipitation. It’s usually made of some sort of coated nylon or some other waterproof/breathable membrane.

Note that traditional “ski jackets” that combine the insulation and shell layer aren’t as versatile since you can’t use them independently. You’re better off taking a warm fleece and a rain jacket so that you have more options for how to combine and wear all of your layers.

Cold Weather Sleep Systems

If your winter plans call for sleeping outdoors, you should think of your sleep system in the same way you think about your clothing system – layers. Again, we’re looking to be able to add warmth when needed without overheating and sweating.

For sleep systems, your layers consist of:

Sleeping Bag Liner - A thin, inner layer that goes inside your sleeping bag. High-end ones are made out of silk but there are cheaper options available. These usually add 10-15 degrees of warmth to your sleeping bag, and have the added bonus of keeping your dirty, oily skin off your sleeping bag, prolonging its life. I always carry a Sea to Summit Reactor Liner when I head out in the winter. Sleeping Bag - This is your insulation layer. You want to make sure it’s rated for something colder than the conditions you plan to face. Most sleeping bags are rated to 0°F, 20°F or 40°F. 40-degree bags are too light for most winter camping, but a 0-degree bag or 20-degree bag may be appropriate. Look for “mummy” shaped bags as they tend to be warmer (but offer less wiggle room). Also think about whether you want the fill to be down (warm, compressible but bad when wet) or synthetic (cheaper, not as compressible, works when wet). Outer Shell - An outer shell is something like a bivvy sack or durable wool blanket. This helps protect your sleeping bag and keep it dry, while also adding another 10 degrees of warmth to your sleep system. If you’ll be sleeping near a fire, this layer will prevent embers from landing on your sleeping bag and burning a hole into the insulation while you sleep. I carry the SOL Emergency Bivvy.

Underneath your sleep system, you also need to think about insulation from the ground. Sleeping pads are rated for warmth with their “R-Value.” The pads you might take out during the summer aren’t usually considered warm enough for sleeping on frozen ground or snow. Ideally you could get a second one and stack them on top of each other.

Another option is to make a bed of evergreen tree boughs. Try to strip off just the smaller branches and needles so you’re not sleeping on any sticks. Put a single sleeping pad on top of a few inches of that and you should be fine. Note that stripping trees of their boughs is frowned upon in protected areas and isn’t very “Leave No Trace”-y.

Understanding & Treating Hypothermia

Hypothermia is a major risk whenever you’ll be outside in the cold for extended periods. It doesn’t have to be below freezing for someone to get hypothermia – in many parts of the US, hypothermia is more common in the early spring and late fall than it is in the winter, since people aren’t as prepared for it.

There are two main types of hypothemia:

acute, or fast onset (ie, falling through ice)

subacute, or slow onset (ie, long-term exposure)

While both types of hypothermia are defined by having a lower-than-normal core body temperature, it’s important to understand the mechanism of how the patient’s core got so cold when coming up with a treatment plan.

It’s also important to note that we’re talking about a person’s core body temperature, not their skin temperature. Core temperature can be hard to measure in the backcountry without specialized gear.

Often, a person’s skin may feel cool to the touch, but their core is still warm thanks to the body’s natural shell/core effect, pulling warm blood away from the skin to prevent heat loss.

Prevention & Staying Warm

The best way to treat hypothermia is to prevent it from setting in at all. It can be hard for your body to rewarm itself in cold conditions, so make sure you take steps to keep yourself from getting cold. Don’t let snow accumulate on your jacket or skin while you’re out – brush yourself off and try to stay dry.

It’s also important to keep yourself warm from within – that means keep moving and keep giving your body fuel to burn. If someone is starting to complain that they’re getting cold, the best thing you can do is give them some exercises or camp chores to get them moving and get their body to warm itself.

These can be as simple as wiggling toes, windmilling arms and squeezing fists, or doing squats, jumping jacks or crunches. Some of these simple exercises are also a great way to warm yourself inside your sleeping bag in case you wake up cold during the night.

But of course, your body also needs fuel to provide energy for exercising and shivering. Make sure that you’re staying well fed throughout the day, and be sure to take a sugary snack or drink if you feel yourself starting to get chilly. That will help throw fuel on your body’s fire to kickstart your internal furnace.

Make sure the cold patient is given plenty of sugary snacks so that they have fuel to burn to keep the shivering process in full swing.

Slow onset hypothermia can be kept at bay by staying:

dry and out of the snow

fed and properly nourished

active and moving, not sitting around

Avoid the temptation to have the cold person sit around idly wrapped in a blanket while someone prepares a fire or tries to heat up some water.

According to the chart above from “Hypothermia, Frostbite and other Cold Injuries” by Gordon Giesbrecht, Ph.D, sitting by a fire does nothing to raise core temperature, and most external sources of heat are far less effective at warming a person than simply giving them the energy and the motivation to heat themselves from within.

Mild Hypothermia

If someone doesn’t know how to take care of themselves effectively, they may eventually slip into mild hypothermia. This is characterized by mild changes in mental status usually referred to as the “umbles” – stumbles, mumbles, fumbles, grumbles.

The person is losing their muscle control and higher level thinking. Sometimes people in mild hypothermia will become lethargic and won’t do simple things like zip up their own jacket to warm themselves.

People with acute hypothermia – maybe they fell through the ice or overboard on a boat and had a sudden drop in core temperature – can usually be spontaneously rewarmed. People with more long-term hypothermia that has set in slowly over a longer period are harder to rewarm.

It’s important for you to recognize the early warning signs and take decisive action to get the person out of the cold and wet, and start rewarming them.

If they can take warm, sugary fluids, they should. They should also be stripped of any wet clothing and insulated with warm, dry clothing. Chemical heat packs or warm water bottles on the neck or groin can help warm blood. If the person’s mental status starts to recover, encourage them to perform simple exercises, if they can do so safely.

Severe Hypothermia

In later stages of hypothermia, there’s “paradoxical undressing” where a cold person may start to rip off their clothes because of warm blood rushing back to the skin, making them feel hot. At this point, their core temperature is dangerously low and the person needs to get to a hospital immediately.

There won’t be any shivering and their vital signs like pulse and breathing may be undetectable. A patient at this stage of hypothermia has a very fragile heart rhythm and should be handled very gently and carefully to prevent sending the patient into vfib, where their heart isn’t beating effectively. This will quickly lead to cardiac arrest and potentially death in a remote backcountry situation.

You don’t want to perform CPR or chest compressions on someone who is unconscious from slow-onset hypothermia, even if they don’t have vitals. This is a very serious medical emergency and the patient needs to be brought to a properly-equipped hospital as quickly and carefully as possible.

The same treatment principles apply as with mild hypothermia – get the patient out of the cold, get them dry and start adding as much external heat as you can. Warm water bottles, heat packs and warmed, humidified supplemental oxygen are all called for, as long as they won’t delay evacuation.

Frostbite & Frozen Tissue

While not as severe of an issue as hypothermia, frostbite and associated tissue injury can also be dangerous issues you’ll encounter in cold-weather situations.

The body actual prefers to let frostbite happen – intentionally pulling warm blood away from the skin and extremities – in order to prioritize core warmth and prevent hypothermia.

You can see signs of frostbite start to set in after only a few hours in really cold conditions. If you are wearing tight gloves or boots that limit your circulation, you’re putting yourself at a greater risk. Smoking cigarettes and drinking alcohol both cause blood vessels to constrict which will also contribute to decreasing the flow of warm blood to extremities.

Mild Frostbite

Mild frostbite is characterized by superficial freezing in the outer layers of skin. The area may be pale, cool and numb, but the layers of skin can still slide freely over each other.

Field treatment involves bringing your core temperature back up to reverse the shell/core effect and bring warm blood back to the injury site. External heat can be applied with chemical packs or hot water, and exercises like windmilling arms can help speed up blood flow to the area.

Severe Frostbite

More severe frostbite is characterized by hard pale or blue skin that doesn’t slide over inner layers. Nearby joints may not move since they’re “frozen” in place.

This is a more complex injury and should ideally be rewarmed in a controlled medical facility. If it will take more than a day to reach help, then consider rewarming the area by immersing it in warm water. Also remember to focus on rewarming the patient’s core temperature to increase blood flow to the skin and extremities.

For both mild and severe frostbite, you do NOT rewarm frozen feet and hands unless you can ensure they won’t refreeze. Allowing the skin to refreeze after it has been thawed can cause devastating tissue death and will likely cause patient to loose the limb.

It’s much better to let someone hike out with a frozen foot than hunker down to rewarm it, let everyone else in your group get cold, and then have the patient try to hike out through the snow with a newly tender and sensitive foot that may refreeze.

The same techniques that prevent hypothermia from setting in – staying warm, dry and well nourished – will go a long way to keeping warm blood in extremities and helping to prevent tissue from freezing.

On the Ice & Around Water

One of the themes you may have noticed is that getting wet is something to be avoided in the winter. Water has a higher specific heat than air, meaning that being submersed in water of a certain temperature will sap heat from your body at a much higher rate than being in air of the same temperature.

This makes it particularly dangerous to be out near bodies of water in the winter. Whether hiking across a frozen river, heading out in a boat or driving around on a frozen lake, you should be prepared to quickly dry off and rewarm yourself in case you fall in.

Falling Through the Ice

There’s an awesome video from a Canadian professor who runs experiments on cold water experiments on himself. Don’t try this at home!

Some takeaways:

The immediate risk from falling in is that you’ll gasp for air and suck down the water, drowning immediately. Your first priority is to stay calm and control your breathing. You have more time than you think to figure out how to get out. Depending on your size and conditioning, you’ll have 2-5 minutes of useful muscle function. If you fell through the ice, your best bet is to get out going back the way you came, since you know that ice was strong enough to support your weight before. Lift your feet up to the surface and kick your feet to slide horizontally out and onto the ice. Use your arms to army crawl forward, or roll like a log to keep your weight spread out. If you aren’t able to pull yourself out, try to lift as much of your torso out as you can and hold still. If you freeze your arms or beard to the ice, you stand a much better chance of being rescued before the hypothermia kills you, which can take a few hours. If you pass out without being frozen to the ice, you’ll slip under and drown much more quickly.

Assisting Someone Else Who Has Fallen In

If you come across a scene where someone else is in the water, STOP! Remember that the person in the water has a few minutes. You’re much better off staying back and coaching the person out of the water than rushing in yourself and becoming another patient.

Call for help and try to assist them from a distance, without putting yourself at risk. There are many sad stories of rescuers dying while trying to rush to someone’s aid, like 4 rescuers who died trying to save 3 campers at a winter camp.

You can use something long like a branch, extension cord or ladder to pull the person out and across the ice. Adding a loop at the end of any rope will make it easier for the person to loop over their head, rather than having to hold on tight.

If someone has been underwater for less than an hour, many rescue protocols say that they are still savable. “You’re not dead until you’re warm and dead,” the saying goes.

When the brain gets cold it uses less oxygen and can subsequently survive being trapped without air for shockingly long amounts of time. Don’t give up on someone after a few minutes.

More Information & Sources

That’s 2500 words on some of the most important risks you’ll face when you head out in the winter. Hopefully now you’ll be better prepared for a safe and fun outdoor adventure in the cold!

Be sure to share this article with anyone in your family who spends time outside in the winter. It may just save their life.

Sources for this article include my own Wilderness First Responder training, as well as MIT Outing Club’s Winter School and first-hand experience I’ve had out in the cold of New England winters.

For more information, check out “The Science of Freezing” from Outside Magazine. Dr. Gordon Giesbrecht, Ph.D is the professor who fell through the ice in the video and also wrote the book that I grabbed that chart for rewarming from.