Thermal Layers and Shell Clothing

 

Clothing for winter in the northern wilderness must cope with a wide range of temperatures, from around freezing to -50^oC (-58^oF) or lower.  Your clothing may also have to fend off serious wind-chill, when travelling by snow machine or skiing across barren terrain such as the Hardanger Vidda in Norway. Your body core must be kept warm to prevent hypothermia and unless your core is warm enough, your extremities are more likely to suffer cold injuries. At times, both in the northern forest and on the northern fells, you will be working hard and generating a lot of heat. At other times, you will be stationary and need a lot of protection from the winter environment. Your clothing system therefore needs to be flexible. Your clothes must be able to minimise heat loss but they must also cope well with perspiration and be easily vented. Outdoor life in winter is tough and your clothes need to be well-made and durable. Another feature of life in the north is fire and hot stoves. Care must be taken with clothing made from synthetic materials that are easily melted as they can be damaged by heat in an instant.

This is the first of two articles on clothing for the northern wilderness. The second will cover footwear, handwear and headwear. You’ll get the most out of this article if you also read my article on heat loss and my article on how to dress for cold weather. Don’t worry, you can read them later. I’ll remind you at the end!

L is for Layers
Layering your clothing is a key principle for staying warm in the winter. Your clothes don’t add heat to your body, they keep you warm by minimising heat loss via conduction, convection, evaporation, and radiation. Air is a good insulator and in addition to air being held within your garments, by layering your clothes you also trap air between your garments. Multiple layers allow flexibility in dressing for varying degrees of cold and activity levels. In a previous article I covered the general principles of how to dress for cold weather. If you have read this article, you’ll remember the acronym COLD. L reminds us that our clothing must be layered.

Wool or Synthetic Base Layers?
You have two broad choices of material for thermal undergarments – wool or synthetic. While the fast moisture-wicking properties of synthetic undergarments are great for high intensity activities such as nordic ski racing, synthetic undergarments have a tendency to smell really bad after only a day or so of wear. Wool on the other hand does not smell bad even after weeks of wear. Moreover, wool garments can be aired for a short while and smell remarkably fresh afterwards. Wool also wicks moisture away from the skin. Wool stays warm when it is wet (up to a point) and, due to an exothermic reaction, actually gives off heat when it becomes damp. Wool has a reputation for being itchy but merino wool fibres are much finer and generally don’t cause any skin irritation. Wool, however, is not very tough. This means that some manufacturers such as Woolpower, add some synthetic materials to the wool to make it both more wear-resistant and machine-washable. Fine wool garments being easily damaged also means that you should avoid wearing them as an outer layer. You should wear at least a light shell layer over the top to prevent snags and pulls to the wool clothing. Wool is heat and fire-resistant though, which makes it good for wearing around hot stoves in cabins and tents. While it’s not critical, you can also buy merino wool underpants, which are warm and comfortable. Good quality wool thermal layers and underwear are produced by Woolpower, Icebreaker, Devold, Janus and Howies.

How to Layer Winter Clothing

The first thermal layer, or base layer, next to your skin should both insulate and wick moisture away from your skin.  Water conducts heat away from your body 25 times faster than air so your clothing’s job of transporting water away from your skin is a critical one. A 200g/m2 top and long-johns from Woolpower are ideal. These garments are surprisingly light in weight. The terry-knit of their base layers makes it warmer for the weight than other woven merino base-layers I’ve tried. 

The second thermal layer, or mid-layer, is designed to trap more air. It is generally heavier than the first layer.  Woolpower’s 400g garment works well for this. A second thermal layer for your torso is needed more often than for your legs.

A third thermal layer can be taken – a knitted wool pullover, a fleece jacket or a lightweight synthetic duvet jacket – that can be worn over the first and/or second thermal layer to add warmth and flexibility to your clothing system. One advantage of a light synthetic duvet jacket is that the outer fabric will shed snow very well, whereas snow sticks to wool and fleece. This jacket can be worn over just the first thermal layer as an outer shell while digging snow holes or qunizes. It will also dry quickly.

Shell Layer
To minimise heat loss, a wind-proof protective shell layer should be worn over your thermal layers. The warm air trapped in your thermal layers must be kept there and a wind-proof shell will prevent this warm air from being displaced. Your shell layer also traps air between it and the thermal layer underneath, adding further insulation to your body. Your shell layer protects your thermal layers from environmental moisture and snow (snow sticks to wool very easily). As mentioned above, a shell layer also protects your thermal layers from wear and tear.

The shell layer can consist of a windproof material such as tightly woven cotton, Ventile, Gore-Tex or a similar material. Ventile and other tightly woven cotton fabrics are the most breathable of shell materials in extreme cold. 

A cotton jacket is my first choice if I don’t expect wet precipitation. If rain or sleet are a possibility then you need raingear that will protect you from this. Your jacket should be roomy. It should be loose (remember L in COLD is for layered and loose) enough to accommodate your thermal layers underneath, as well as spare gloves, hats and personal equipment in the pockets. A belt around the waist on the outside of a loose smock is effective in retaining warm air around your torso. Another feature to look out for is a generous hood that can accommodate your largest hat. A fur trim helps keep warm air near to your face. For really bad conditions, a snorkel-type hood is very good. Make sure it will turn with your head so you don’t end up looking at the inside of your hood every time you want to look left or right. The cuffs of your jacket should be roomy enough to accommodate gloves and have a secure fastening that will seal the sleeve around your wrist. This fastening should be easily adjusted.

There are many manufacturers of cotton smocks. Mine is a Norrona Arktis Anojakke that no longer features on Norrona’s website. I fear that this excellent jacket is no longer made.  For Ventile there are number of good manufacturers and another option is to buy the material and have a jacket made to an existing pattern or even your own design.

For trousers the choice is less critical with respect to breathability as you sweat less on your legs. I make a decision based on how much time I’m likely to be spending in the snow, for example digging out snow shelters, and in the latter case I have a preference for tough Gore-Tex trousers. I find kneeling on snow in cotton trousers melts snow into the fabric, whereas this doesn’t happen with Gore-Tex. You need to be more careful with Gore-Tex and similar fabrics near fires and stoves of course. Braces are a really good idea in the north. Even better if your trousers have a high waist. This combination keeps your trousers high on your mid-section which, with no chilling draughts on your lower back, remains snug.

 

Top Thermal layer or ‘Mothership’ Jacket.
Your mothership jacket is one that can go on over the top of everything else. It should have an insulating material such as Primaloft or down and a wind resistant outer material. Useful when you are waiting to head out for the day or have stopped for a break, you can throw this jacket on and off easily without re-arranging any other layers. A mothership is also good for travelling by snow machine when you need all the insulation you can muster.  When not being worn, you can stow it in a place that is easily accessible.

When ski-touring I keep a synthetic duvet jacket (one size bigger than my normal) at the top of my pack to put on quickly over everything else when stopped for a break. I’ve had to wear this jacket inside cabins they have been so cold when I’ve arrived. In the northern forest, I use a Swedish military M90 jacket, as it is long enough to insulate my whole body core rather than just down to my waist. In really cold temperatures I find this longer design more comfortable than jackets that are cut higher.  Your mothership also makes an excellent pillow.

Manage your clothes.
Remember, however good your clothing is, you will only get the most out of it if you learn to manage it properly. You can manage your temperature and minimise sweat by adjusting layers, ventilating and regulating activity.

Adjusting layers: Be bold, start cold. Before exertion, take layers off and start a little cold. The exertion will soon warm you up. After exercise, put layers back on before you start to feel cold. Having a mothership jacket makes this easier.

Ventilation: Open up front zips, expose the neck, use ventilation holes (e.g. some clothing has zipped ventilation holes in the armpits), loosen sleeves or even roll them up. Again, try to do this before you exert yourself. Adjust as necessary during exercise.

Regulation: if you are still getting hot and sweaty despite the above measures then you should probably slow down a bit and pace yourself. Apart from pumping moisture into your clothing, you are possibly working at a rate that will leave you exhausted in a relatively short period of time. Low-blood sugar (hypoglycaemia) is a significant factor in susceptibility to hypothermia.

Learn From Experience

Everyone is different and will be warmer or colder than others at different times and during different activities.  Learn to use your clothing to its best potential through experience.  Having a flexible and well thought-out clothing outfit will help you to stay warm but not get too warm.

Picture credits – the author owns the copyright for all images in this article.

To get the most out of the above article, you should also read:

The Four Horsemen of Heat Loss

How to Dress for the Cold: COLD or COLDER…

Related Articles On Paul Kirtley’s Blog:

Clothing for the Northern Wilderness Part 2 covers protection for hands, feet and head.

Take Care When you Enter the Blue Zone

A Winter Camping Trip in the Northern Forest