The Science of Staying Warm In Cold Weather

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Too many people think once it gets cold outside, they can’t enjoy outdoor activities like hiking, camping, biking, skiing or snowboarding, snowshoeing, or trail running.

If you wear the right gear and take deliberate actions to fend of the cold, staying warm enough to enjoy yourself in almost any weather isn’t a problem. Even my wife, who has Raynaud’s and runs at a pretty cold temp, enjoys night skiing with me.

The science of staying warm

I’ll save you the full thermodynamics lesson for another day, but staying warm boils down to two things:

  1. Getting heat to all your body parts
  2. Retaining the body heat you generate.

It sounds simple – and it is – but you have to think logically through these processes to understand why you get cold and how to stay warm.

It takes more than just throwing on a few more layers to stay warm in cold weather – in fact, adding more layers may be the exact wrong thing to do. We’ll discuss that more later on.

Getting heat to all your body parts

Keep those toes warm

Some of the hardest parts to keep warm on most people are your fingers, toes, ears, and nose – and for logical reasons. Here are the reasons why these parts get cold first:

  • They’re not crucial to survival -The human body operates in a narrow temperature range. If our core temperature gets below about 85° F, we’ll go unconscious and likely die. Our vital organs such as our heart and brain don’t operate properly if they drop below about 89° F. To prevent this, our bodies automatically shunt warm blood to the vital organs when they sense the extremities getting cold. This helps keep those organs warm and also prevents heat-loss when blood goes near our cold skin surface. That’s a good thing because it keeps you alive, but it means your toes are going to be cold unless you do something about it.
  • They’re in exposed locations – Our fingers, toes, ears, and nose are all on parts of our body that can be hard to keep fully covered and insulated. We’re limited in how much insulation we can add inside our shoes or boots. Our hands usually need to have some level of dexterity which limits our options for covering them. Our ears and face need to be somewhat exposed to allow us to hear and breathe properly.
  • They have higher surface-to-volume ratios than other body parts – These parts have a lot of skin and relatively little tissue mass compared with parts like our legs or arms. This means more surface area to lose heat from.
  • They have blood vessels that are easily compressed – Blood is the method our bodies use to transport heat from our muscles and organs out to our skin and other parts. If we constrict blood vessels by wearing too tight of fitting clothes, we get cold.
  • They’re further away from your heart – Warm blood comes from the heart and it has a much longer distance to travel to get to your toes than it does to get to your back. This means the blood getting to your toes isn’t as warm as it is closer to your core.

Our bodies are excellent at automatically adjusting to account for all these issues, but we can take actions to tell our bodies it’s safe to keep our toes and fingers warm.

So what do you do? You keep your core temperature up, reduce heat loss at your skin surface, improve blood circulation and limit blood vessel constriction. We do all this by staying active and wearing the proper clothes. We’ll discuss these topics in more depth so keep reading.

More on Improving circulation

Even if you have the ideal layering systems going on, if you can’t get warm blood out to your toes, they’ll still be cold. To improve circulation to your extremities can be hard if you have naturally poor circulation to begin with. If that’s you, there are a few things to consider. Look here as a starting point.

After that, let’s look at what you can do while out on your adventures. Circulation tends to decrease when you sit still. This is exactly what you do on the lift, in the car, in your tent, or while you’re taking a rest break. To remedy this you can pump your fists, wave your arms around, or generally try to keep your limbs moving. Keeping your hands below your heart will also help. Sometimes spinning your arms like a windmill can do wonders to get the blood moving out to your fingertips. Jumping jacks or dance parties can look funny to observes, but who cares if you’re staying warm and having fun, right?

keep cold fingers warm
People with very poor circulation

Circulation also decreases when the vessels in your body get obstructed or compressed. This is easy to overlook when skiing since we want to put on big, heavy socks inside our tight ski boots and often wear multiple layers of gloves. If you’re guilty of layering on two pairs of wool socks or three pairs of gloves until your toes have no room to move, but they’re still cold, they likely aren’t getting any blood flow and will not stay warm.

To fix this, you need to give them some space. Use mittens that have plenty of room for your hands and don’t have a wrist band that could double as a tourniquet. For your feet, the best solution is to get a custom boot fitting. Pricey, yes, but it will make you love your boots forevermore. Learn about custom boot fitting here.

If you’re not up for that, you can try some other tricks I’ve learned over the years. Pick up a pair of dedicated ski socks. They’re designed for ski boots and have padding where you need it but not where you don’t. If you get them a bit bigger than normal, but not big enough to bunch up, and then pull them away from your toes a bit when you put them on, you’ll avoid restricting your blood flow as much.

warm wool socks
Good socks can make a huge difference

Thicker socks don’t mean warmer socks if your toes aren’t getting any heat. I like to wear thinner wool socks that allow my toes to get good blood flow and therefore (heat).

Stoking the fire

eat fatty snacks to stay warm
Fatty foods like nuts help your body stay warm

Another consideration in staying warm is ensuring your furnace has enough fuel to keep up with your body’s needs. If you don’t eat enough or stay hydrated, you’ll get cold. Your body needs fuel to generate heat. The best strategy is to eat slow-burning fuel sources in small, frequent quantities throughout the day. If you eat too much all at once, blood will be shunted to your stomach to aid in digestion at the expense of your toes and fingers.

Snacking on trail mix, cheese, beef jerky, or other fatty snacks is ideal.

If you get dehydrated, your blood thickens and your body is less effective at circulation. Be sure to bring and drink plenty of water with you. If you want to double-dip, you can bring a thermos of hot chocolate made with whole milk. This gives you some fatty fuel as well as water and as a bonus, adds an external heat source to help supplement your own engine.

So these tips will go a long way to getting heat to all your body parts, but that’s only half the equation.

How to retain the heat you produce

Retaining all the heat your body generates is critical to staying warm when out and about in cold weather. To do this we need to reduce heat transfer from our bodies to the environment. The two main methods of reducing heat transfer are keeping things dry and insulating them. Again, this isn’t a lecture on thermodynamics, but the basics are that insulation reduces the loss of heat to the cold air, and staying dry makes all our insulation layers much more effective since water is a better conductor of heat than air – 50 to 100 times better!

How to stay dry

Let’s start with staying dry. When things get wet, whether that means rain, snow, or sleet, the need is the same – don’t let your insulation layers get wet. When playing in bodies of water when surfing, canyoneering, kayaking, or swimming, the equation is a bit different.

Insulation works by preventing the transfer of heat from the hotter side to the cooler side. In winter that means keeping the heat near your body. Air doesn’t transfer heat nearly as well as water so keeping water out of our insulating layers is key.

When adventuring, water tends to come from two places:

  1. The external environment
  2. Your own body

Keeping external water out is pretty easy. The first option is to stay out of the rain, snow, or sleet. Since that’s not always conducive to chasing awesome powder or getting to your campsite before dark, we have some other options. Waterproof external shells work really well at keeping us dry, so pick up some waterproof gear for whatever activities you do and keep the water out.

Keeping water out is easier than getting rid of water already inside our layers

Water from your own body comes in the form of sweat (liquid or evaporated as water vapor) and exhaled water vapor. As I mentioned earlier, our bodies work hard to operate in the ideal temperature range and when we get too hot, we automatically try to cool off by sending blood (heat) to the extremities by opening up the blood vessels and capillaries. If that’s not enough to bring the temperature down, we start to sweat to enhance the heat transfer away from our bodies. The problem with sweat is that it doesn’t evaporate well when it’s trapped in a layer of fabric. That leads to too much heat being lost and we end up shivering as soon as we stop moving.

The trick to avoiding this wet situation is to not sweat in the first place. We do that by pacing ourselves in cold-weather activities as well as wearing the right layers. An example is when I go backcountry skiing. I don’t want to pace myself there because the friends I ski with are fast enough as it is and I’m usually at the back of the pack. Instead, I have to wear clothes that keep me from sweating in the first place. Sometimes all I wear is a thin pair of technical pants and a long-sleeve breathable technical shirt. No hat, no gloves, and no vest. If it’s a bit colder, I’ll throw on a puffy vest to keep my core temp up, but I keep my arms uncovered because they sweat a lot and keeping them uncovered helps me shed excess heat quickly.

I have quick access to warmer layers in my pack for when I stop, but when I’m moving, my goal is to stay dry. If I feel I’m too cold or too hot, I’ll adjust with zippers or thin layers until I get it right. Just pay attention and adjust as needed throughout the day.

What if you get wet anyway?

So you take all the precautions to not get all sweaty, but you do anyway. This is where choosing the right fabric types is critical. You need fabrics that don’t absorb moisture, allow water vapor to escape (breathability), and wick moisture away from your body. Each layer you use will be a bit different, but all should have these types of properties to varying degrees.

A ton of proprietary fabrics exist that consist of varying blends of existing fabrics with different treatments and such. We won’t cover them all, but let’s look at some of the more common fabric types and how to use (or not use) them.

Cotton – is terrible for staying warm because it readily absorbs moisture. Avoid cotton for cold weather activities. If you have cotton socks, they can make your feet cold even if the rest of you is toasty warm because they’ll absorb all the water your feet sweat out and then suck heat out at a ridiculous rate. Cotton = instant cold toes if you sweat at all.

cotton isn't good for staying warm
Cotton makes for poor technical fabric

Wool – is an amazing natural fiber that you should own. The material creates pockets that trap air, so it’s awesome at regulating heat and staying warm. (Bonus: It also keeps you cool in hot weather) It’s also breathable and wicks moisture. You can’t really go too wrong with wool as an insulating or base layer. It’s not great as an external layer, but I love a good pair of wool socks, a balaclava, or as a base layer when blended with other fabrics. To make wool even more awesome, wool doesn’t retain odors.

wool keeps you warm
Wool is designed by nature for staying warm in cold weather

Bamboo – is an up-and-coming fabric touted for its renewability. It’s considered synthetic because of the way it is processed. Bamboo feels light, breathable, and moisture-wicking—it also protects your skin from ultraviolet rays. I don’t have much experience with bamboo fabrics since I don’t see many advantages to it over wool, but it may work for those opposed to using wool for whatever reason.

bamboo makes warm fabric
Bamboo can be used if you don’t like wool

Nylon – is perhaps the most widely used fabric in outdoor equipment like backpacks and such, the synthetic fabric is soft as silk, mildew resistant, and dries quickly. It’s also breathable and wicks sweat from your skin to the fabric’s surface, where it can evaporate. Nylon can make some good layers when blended with other fabrics but isn’t the warmest fabric around.

nylon stays dry
Nylon is primarily used in outer layers

Polyester – is very common among outdoor fabrics and can be found on most labels as a blend with other fabrics. It’s basically plastic cloth, it’s durable, wrinkle-resistant, lightweight, breathable, and non-absorbent, which means that moisture from your skin evaporates instead of being drawn into the material. Polyester also repels UV rays and insulates you even when it’s wet. Polyester isn’t the warmest fabric and also tends to retain smells.

Polyester fabrics are common in athletic wear

Polypropylene – is made from plastic and is completely water-resistant. It is usually used as a base layer so that even after building up a sweat, what’s touching you is completely dry. Polypropylene forces moisture to pass through its fibers, expelling it to the fabric’s surface where it can evaporate. Like polyester, it’s not super warm, but can make a good blended material for a base layer.

polypropylene fabric
Polypropylene is a kind of plastic

Spandex – (also known by the brand name Lycra) puts the stretch in workout wear. The synthetic fabric can expand to nearly 600 percent of its size, offers an unrestricted range of motion, and then snaps back in place. Spandex is also breathable, wicks moisture, and dries quickly. It’s used as a blend in many base layers because of the stretch.

spandex fabric
Spandex is common in technical base layers

Many other patented fabrics exist that you’ll find on clothing labels, but what characteristics you need to look for depend on what layer you’re shopping for. Layering your clothing is important because it gives you options. You can add or remove layers depending on the situation you’re in. Wearing multiple layers also provides better insulation than a single thick layer because it creates more pockets of warm air with less material and weight.

Let’s look at a good layering system for staying warm in cold weather.

Base Layer

The base layer is the layer right against your skin. Its main function is to keep you dry, comfortable, and also adds insulation value, but typically not too much unless you opt for thicker base materials like these awesome wool thermals

Base layers should always be moisture-wicking and stretchable meaning they usually have some amount of spandex in them. I like these as my base layer for most situations:

I like these because they’re not too heavy, they breathe well, and they keep me warm. I’m typically very active when I’m out and about, so I like the lightweight wool base layers. If I’m going winter camping or something like that where I’ll likely be sitting still for a long time, I may prefer a heavier weight-base layer. In my opinion, nothing beats 100% merino wool.

Insulating Layer

The insulating layer is next and it should be as warm as the situation calls for. It doesn’t have to be waterproof on the outside, but it should be breathable to allow water vapor to escape. Typical insulating layers I use are down puffy jackets, wool, fleece, or synthetic insulation layers. Insulating layers should be lightweight for most outdoor activities and should be thick. The extra thickness is what insulates you by creating layers of air pockets. Down is probably the best insulating material because it has all these properties and it packs away super small so you can fit it in your pack when you don’t need it. It’s also the most expensive, but if you want to stay warm, it’s worth it.

Keep insulating layers dry to stay warm. If it’s snowing or raining, or you’ll be down on the wet ground, be sure to cover them with an outer shell layer. If they get wet, they will be much less effective at keeping you warm.

When the weather is warm enough or you’re working hard enough, you don’t need an insulating layer, but if you’re out in cold environments, it’s a good idea to have one packed away just in case you get stuck and need to stay in one spot for long. You can get surprisingly cold even when the air temp is in the 60’s.

A vest is also good to have so you can insulate your core, but keep your arms out for better ventilation.

Outer Layer

Your outer shell is the final piece of the puzzle to staying warm. Its job is to keep you dry and block the wind. It must also be able to breathe or all your other layers will fill up with sweat and water vapor like a greenhouse. Wind can suck a lot of heat out of you very quickly. Think about that fan in the summertime.

Several different types of fabric can make good shell layers, but the gold standard is Gore-Tex. It can breathe but is also very water-resistant. Be sure you have a good water-resistant layer on any parts that can get wet. That includes shoes, gaiters, pants, jackets, hats, and gloves. If you have a nice Gore-Tex jacket and pants, but you wear your ultralight, breathable trail running shoes on a winter hike, your feet and socks will be wet before too long and you’ll be cold.

Outer layers can typically be pretty thin and lightweight but sometimes come combined with insulating properties. I find the most versatility in having the outer layer separable from any insulating layers to allow more flexibility in matching the needs of the day.

Some people like insulated pants, but I tend to get way too hot in them. I opt for just a pant shell and look for ones that have vent zippers if I get too hot. If I’m doing something very cold, it’s easy to add a layer of fleece pants. Just don’t put on your cotton sweat pants because they don’t breathe at all and will just absorb all your sweat.

Covering your face and ears

We’ve covered how to dress up almost all of your body, but what about your face and ears? They often get cold because they’re hard to cover. Ears are easier than your face to cover. Simply use a balaclava or ear warmer headband like these – again – merino wool.

When it comes to your nose and mouth, the challenge is that you exhale a lot of water as you breathe. Anything you put over your face will get wet if you don’t have a clear pathway for exhalation. If I don’t need to cover my mouth and nose for warmth, I don’t. The only time I do is when it’s very very cold. In those cases, I typically pack a spare face mask so I have a dry one when the first gets wet and freezes solid. I’ll swap it out and put it in a pocket near my body to keep it from freezing and help it dry out.

Additional tips for staying warm

Take frequent bathroom breaks. Keeping all the extra liquid inside you only means more mass to keep warm for your body. Pee it out as needed and you’ll stay warmer.

Get well-insulated boots. Especially the sole. You can lose a lot of heat to the ground through your rubber boot soles. Pick up a set of wool insoles to keep your feet warmer.

Dry out your clothes 100% before and during your adventures. If your gear is wet, you’ll pay the price by not staying warm. Dry out your shoes or boots before you head out and do everything you can to keep them dry.

Carry spare gloves and a spare hat. This goes with keeping everything dry, but spares give you options if you do happen to get wet or you lose something.

Avoid sitting on bare ground, even if it’s dry. Rocks, logs, snow, and dirt will suck a lot of heat out of you quickly if they’re cold. If you need to sit down to take a rest, sit on your pack.

Stay in the sun. If the sun is out, you’ll stay warmer if you consciously turn your broadest side directly toward the sun. This is usually your face and chest.

Along with turning toward the sun, if you wear dark colors, you’ll absorb more heat from the sun. Black is my preferred color when I know it will be sunny and cold out.

Plan ahead. It’s easy to think that it will only be 9° F at the start of your trail run, that you should bundle up more. The problem is that after a few minutes you’ll be too hot. I like to start colder than I prefer and then warm up as I go when I’m doing very active things. If I’ll be less active, like a day at the ski resort, I’ll bundle up from the beginning and then shed layers as needed.

I hope all these tips will help you in staying warm out there in cold-weather adventures and open up the door to let you enjoy more months of the year. If you think through the why’s of staying warm it becomes much easier to figure out how to do it.

If you have other tips on staying warm that I’ve missed, leave them below in the comments for other readers to benefit from.

staying warm in the sun
The sun can make a huge difference on a cold day

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