How to dress for cold weather

Reading time: 15 minutes

Recap

Wear multiple breathable and quick-drying layers;
Avoid fabrics such as cotton and linen;
Use merino wool as base layers and wear 100% wool socks;
Avoid getting wet by sweating. Regulate the microclimate around your body putting layers on and off;
For boots: take two sizes bigger;
Gloves: take a spare with you.

““Is it cold outside?””

A question you’ve probably heard many times. The most common mistakes people make by choosing the right clothing for the cold, is by looking at the temperature that the weather forecast provides, and by choosing only one thick jacket instead of multiple layers.

But there are multiple factors that influence the RealFeel temperature: how the temperature actually feels outside. In this in-depth article, I will address several aspects of thermoregulation, and how you can stay warm in (extreme) cold weather conditions by picking the right clothing. This article is divided in three chapters: key elements, fabrics, and layering system.

Grab a coffee or tea and prepare yourself for a long read. But it will be worth your time. I promise.

CHAPTER 1: Key elements

1.1 Windchill

This is the temperature that a person feels because of the wind. It works the same as we blow on hot soup if it's too hot to eat, or when we turn on a fan during summer to get a cool breeze. The movement of air increases the loss of heat by convection.

The combination of wind and low temperature in winter can be deadly. Wind chills below minus 20 degrees can result in frostbite within a minute of exposure.

1.2 Humidity

Humidity is the presence of water molecules in air. In cold weather, high humidity levels will make you feel colder. A dry -20 degree Celsius feels less cold than a humid -12 degree Celsius. This is because water removes body heat 20 times quicker than air.

Cold air can’t retain as much moisture as warm air, so it's less common in cold weather to have high humidity levels. But if you live in a region next to the sea like Helsinki - with a humid continental climate - you might experience higher humidity levels during the winter than usual.

1.3 Elevation

The higher the elevation, the colder the temperature. If there's no snow or rain falling from the sky and you’re not in a cloud, then the temperature decreases approximately
9.8°C per 1000 metres (or 5.4°F/1,000 feet)

If you’re in a cloud, or it is snowing or raining, the temperature decreases approximately
6°C per 1,000 metres (or 3.3°F/1,000 feet)

1.4 Activity

When we dress for colder weather conditions, we want to create a micro-climate around our body which we can control by activity and by putting layers on or off. The key to creating this microclimate is layering multiple layers of the appropriate fabric.

“They key to creating a microclimate around your body is layering multiple layers of appropriate fabric. ”

CHAPTER 2: Fabrics

So what are appropriate fabrics? When you are layering up for (extreme) cold weather conditions, it is important to understand the characteristics of certain fabrics. You want to avoid fabrics such as cotton and linen, as they absorb moisture quickly, but dry very slowly. Wearing a damp or wet cotton T-shirt in cold weather conditions can lead to hypothermia as it literally sucks the heat out of your body.

““It’s important to choose quick-drying materials.” ”

It's important to choose quick-drying materials. Synthetic fabrics often dry quickly, but the downside of synthetic fabric is that it will stink after absorbing a bit of sweat. My personal preference is (merino) wool. Wool is moisture-wicking, quick-drying, and keeps its insulating properties when wet. It even becomes a bit warm when it gets damp. It doesn't stink after many days of use, and it's also anti-bacterial. I will briefly describe a few insulation materials.

2.1 Down

A down jacket has little pockets filled with down and feathers. The air gaps between the down and feathers will keep the warmth. The fill power or fluffiness is measured in CUIN. The higher the CUIN, the higher the insulation.

The downside of down is that it doesn't withstand moisture very well. If down feathers become wet, they will clot and create cold spots. This works the same with down sleeping bags. Down insulates very well, but if you compress the air gaps between the feathers by laying on them, it will lose its insulating properties and will create cold spots. Therefore, I prefer a sleeping bag with down on the upper part of the sleeping bag, but another form of insulation (like G-loft) on the lower part.

When buying a down jacket, also keep an eye on the amount and the direction of seams. Seams are cold spots as well.

““The downside of down is that it doesn’t withstand moisture very well.””

Down jackets can be your best insulation layer. They are lightweight and compact, but I wouldn't wear it as an outer layer in wet conditions or when I have to 'bushwhack' through the wilderness. If you want something more durable, I would recommend going for a wool pullover or a fleece jacket.

Most of the time, a down jacket is a fragile jacket. If it gets a puncture from a bush in a forest, you will loose down feathers. The toughness of a jacket depends on the denier: the thickness of the outer fabric. Fabrics with a high denier count tend to be thick, sturdy, and durable. For instance, a 200 denier (200D) is lightweight, whereas a 500 denier (500D) is more heavy-duty. Also the way the fabric it's woven plays a role. Ripstop is a special reinforcing technique that makes the fabric resistant to tearing and ripping. So if you see a down jacket that has a 60D ripstop outer fabric, you know what it is!

2.2 Wool

Again, wool is a popular fabric among outdoor people. Especially among those outdoorsy people who like bushcraft and wild camping. It might be less popular for mountaineers or long-distance hikers, as it is heavier than a synthetic fleece or down jacket. I'd say a wool pullover is more durable and more versatile.

“Wool is a versatile and durable fabric.”

The downsides of wool are that it's more expensive than synthetic materials and it needs more care. You shouldn't wash it too often and you can't tumble dry it. Merino wool has specific wool care instructions, and if you want to enjoy your merino wool clothing for a long time, you should take care of it and follow the instructions.

2.3 Fleece

A fleece jacket is a lightweight jacket made of synthetic polyester material or sometimes a polyester and wool blend. It's lighter than wool, and it dries quickly. It has good insulation properties, but it often doesn't breathe as easily, meaning it will trap moisture and sweat. It's also more flammable than wool. It's a great alternative for those allergic to wool.

There is a lot of different fleeces on the market, but I typically distinguish two types of fleeces: microfleece and polar fleece.

“Fleece is a great alternative for those allergic to wool.”

Micro fleece refers specifically to the thinnest and most flexible of all the fleece thicknesses. It's often 100% polyester, and because it's lightweight and does an excellent job of wicking moisture away from the body, microfleece is a popular choice for activity. It is resilient enough for everyday use as well as for high-performance activities such as mountaineering.

Polar fleece is much thicker and warmer than microfleece. They are great for colder weather conditions.

I'm a fan of Polartec fleece material. Polartec fleece provides warmth without additional weight and is also hydrophobic. This means the fabric absorbs less than 1% of water. There are over 100 types of Polartec fabrics, which can be found right here

Polartec itself doesn't make fleeces, but they partner up with brands such as Mountain Hardware, Arc'teryx, Rab, and many other brands. You can find Polartec fleece fabric in many fleece jackets. Just look for their logo!

CHAPTER 3: Layering

As I mentioned earlier, the key to creating a breathable and quick-drying micro-climate around your body is layering. So how does layering work?

3.1 Baselayer

The very first layer which has direct contact with your skin is called the base layer. I highly recommend picking a 100% merino wool base layer. This layer will absorb your perspiration (sweat) directly and will keep your mid-layer dry.

3.2 Midlayer(s)

The second, third and maybe even fourth layer are called mid-layers. These layers have one goal: insulation. Your mid-layer can be either from synthetic materials (e.g. fleece) or natural materials (wool, down, etc.). I still don't recommend using cotton or linen. It's important that this layer can trap air, but is also breathable. A layer can trap air if there is space for air, so don't take a too tight mid-layer that compresses all the air.

3.3 Outer Layer

The layer that's on top of your mid-layer(s), is called the outer layer. They often call this a hardshell. This layer has to withstand the harsh elements that nature exposes. It has to be a windbreaker and a waterproof but breathable layer. This layer is often thin and doesn't have insulating materials.

Breathability is extra important with this layer. What happens when you put a plastic bag over a plant? Indeed: the humidity level around that plant increases and moisture will collect on the inside of the plastic bag.

Your body isn't any different. It breathes moisture and it needs air gaps for moisture to escape. So not any regular raincoat will do the job. It's really important (!) to have a breathable hardshell, because if it's not breathable, moisture will collect on the inside and it will make your mid-layer(s) wet, and you will become cold.

I can recommend GoreTex hard shells or EcoShell from Fjallraven. I've experienced that GoreTex is tougher than EcoShell, but I really like EcoShell because their jackets are soft and silent. GoreTex hard shells often make more sound when you move. Both do a really good job.

All hard shells have a Durable Water Repellent (DWR) coating. The function of this coating is to repel water off your jacket so it doesn't become soaked. When the DWR coating breaks down, the rain jacket's exterior becomes waterlogged and heavy. It will also lose its breathability.
It's important to maintain this DWR coating. You can test if the DWR coating is still good by spraying water on your jacket and check if the water rolls off. If it doesn't roll off: give your jacket a good shake. Does the water fly off? Your DWR is in good condition.

Ok, I hope that wasn't too much information to process. But it's really important that you understand the concept of layering and how fabric works. So I'm not finished yet. We are almost there!

3.4 Reinforcement layer

Alpinist may call this a belay jacket, and some will call it a polar parka. But when you are dealing with very cold weather conditions - I would say -15 degrees Celsius and below - you might look into getting a belay jacket. It's an extra layer that goes on top of all of your jackets and you mainly put it on when you inactive or and/or feel cold. In Northern Finland, I've experienced -37 degrees Celsius in winter and I was wearing my belay jacket all the time.

I find it important that a belay jacket has a hood and insulated pockets for your hands. You will wear this jacket when you are inactive or when it becomes really cold and windy.

Gloves

Overall, I distinguish two types of gloves: finger gloves and mittens. Both have an insulated liner and both have a different function. I use the finger gloves for activities where I need my fingers (for instance, hanging up a hammock or setting up a tent), and I use the mittens to warm up my fingers when I don't need to use them as much. So in general, I'd switch to my mittens when I feel my fingers are getting cold.

The mittens are much warmer than the finger gloves due to the fact that your fingers touch each other and there is an air pocket inside the mitten which can keep your fingers warm.
It's always good to have two pairs of gloves in case one pair of gloves get wet or you lose them. In extremely cold weather conditions, it's really important to have a back-up for the back-up. If you lose your gloves, you may lose your fingers.

Boots

I advise going for a boot with a removable liner inside it. Your boots will get really damp after a long day of hiking in snow and it's important to dry them for the next day.

I'd also advise choosing two sizes bigger than your usual shoe size. This is because you will wear thick wool socks or even two socks on top of each other. Remember that you need air for good insulation. So if you choose a size too small, the boot will compress all the 'air pockets' inside and around your wool socks and will diminish the insulation properties. Also note that with higher elevations, your feet will literally 'grow' a size bigger. Take two sizes bigger.

I personally wear the Hanwag Abisko GTX because they have a GoreTex membrane and a removable inner shoe.

Socks

I've written about the properties of wool earlier. And I recommend wearing wool socks only. Most stores only sell socks with a wool blend (like 60% wool). But in winter conditions, you'd like to have socks made from 100% wool. Real proper granny socks.

Ideally, you wear two pair of thinner socks than one pair of thick wool. This is because two thin socks dry quicker than one thick sock. Wool for the winners.

With all this knowledge about layering and fabrics, you should be good to go to face the extreme cold and stay warm and dry. I hope you've gained some knowledge about layering and outdoor clothing. Your next step? Get your cold-weather gear together and go outside.

Recap

Wear multiple breathable and quick-drying layers;
Avoid fabrics such as cotton and linen;
Use merino wool as base layers and wear 100% wool socks;
Avoid getting wet by sweating. Regulate the microclimate around your body putting layers on and off;
For boots: take two sizes bigger;
Gloves: take a spare with you.