The Science of Clothing Layers for Winter Hiking

The Science of Clothing Layers for Winter Hiking

Wearing multiple clothing layers for winter or cold weather hiking keeps you drier and warm by moving moisture away from your skin. Sounds simple, right? It is, but many people struggle to understand the scientific principles behind layering and how they can guide your baselayer and mid-layer clothing choices for winter hiking. Check out our clothing recommendations below.

Layered Clothing

The core principle behind layering is to dress like an onion, with multiple clothing layers playing different roles in moisture management, heat retention, and weather protection.

  • Baselayer garments are worn directly on your skin and are designed to keep you dry by moving perspiration to the next higher layer, your mid-layer.
  • Mid-layer garments are designed to keep you warm, even though they absorb moisture from your baselayers. Some mid-layer garments are more breathable than others and can dry when worn, while others are designed purely for warmth and are not terribly breathable. We discuss this further below.
  • Finally, an outer shell layer is designed for weather protection, be it wind, rain, or snow.

Evaporative Cooling and Wicking

Baselayer clothing is intended to move moisture, created through perspiration, away from your skin in order to counter a physical process called evaporative cooling. When moisture sits on your skin, it literally sucks the heat out of your body in an attempt to evaporate. This is the reason why perspiration makes you feel cooler in summer.

In winter, you want to move that moisture off your skin and through your baselayer clothing so your skin isn’t in contact with wet fabric. That’s where a mid-layer comes in. The best mid-layers will absorb the moisture passing through your baselayer garments. This is a process called wicking. Ideally, you want a mid-layer that remains warm when it absorbs moisture or multiple mid-layer garments that achieve the same effect.

The underlying mechanism behind wicking is called capillary action, where a liquid is pulled from one layer to another without the influence of gravity. If you’ve ever dipped the corner of a sponge into a pool of water, the water is drawn into the sponge through this process.

The strength of the wicking process between a base layer and a mid-layer depends on the structure of the mid-layer and how absorbent it is. A porous mid-layer, like a fleece pullover, is very effective in pulling moisture out of a baselayer garment because it contains many small pores that suck in moisture like a sponge.

The outermost layer, a shell is usually the least wicking layer and is designed more for wind, rain, or snow protection. It may passively trap some of the warm air that escapes the mid-layer, but it’s usually not insulated.

Dress like an onion, putting on layers when you get cold and taking them off when you get warm.
Dress like an onion, putting on layers when you get cold and taking them off when you get warm.

Clothing Selection Guidelines

Here’s what the science of layering informs us about clothing selection for winter hiking. If you like wool, you’re really going to hate what I’m about to tell you. 

Baselayers

The best baselayers are ones that don’t absorb much perspiration and which can wick it efficiently to your mid-layer. Synthetic jerseys and long underwear are clearcut winners on the score. Thinner baselayer garments are better than thicker ones because the moisture has less distance to travel to your mid-layer. The same holds for more fitted baselayers versus looser-fitting ones. If you can hold up a baselayer jersey and see light coming through it that’s good. It’s even better if you can see the outlines of objects or furniture in the same room.

Synthetic baselayers hold up very well over time, they’re inexpensive, and easy to launder in washing machines. My gotos are REI Active Pursuits Long Sleeve T-Shirt, Nike Dry-Fit Legend Long Sleeve Tee, Helly Hansen LIFA Stripe Crew, and the Helley Hansen LIFA Pant.

Wool baselayers hold onto moisture and take much longer to dry, even though they can feel warmer when they’re damp. As far as layering goes, the primary goal of a baselayer isn’t to keep you warm but to move perspiration off your skin to the next layer. I know people like wearing wool baselayers because they don’t smell as much, but I’m much more interested in wicking performance than body odor on winter hikes when icicles hang off my nose hairs and beard.

Wool baselayers have other issues too, such as high care and maintenance requirements (special soap, hand wash, hang dry), and they have to be replaced much more frequently than synthetic base layers. They are also a lot more expensive. I’m lucky if I can get two years out of a wool jersey, while I can easily get ten years or more out of synthetic ones. That’s a lot less trash in the landfill with none of the associated overhead of animal husbandry.

Wool baselayers made with a combination of wool and synthetic yarns are a better choice than straight wool and there is a whole segment of the outdoor industry working to make wool suck less. Some good examples include  Smartwool Intraknit, Ortovoz Comp Light, Helly Hansen LIFA Merino, and the Nuyarn garments made by KUIU and Artilect.

Fleece hoodies and vests are the bread and butter of winter mid-layers
Fleece hoodies and vests are the bread and butter of winter hiking mid-layers

Mid-layers

Fleece mid-layer pullovers and hoodies are better than wool because they dry quickly when exposed to air. The problem with fleece is that the outdoor industry has come up with so many proprietary variants that it’s impossible to know how well a garment will perform unless you try it in the field. Gone are the days when all fleece was classified as being 100 weight, 200 weight, or 300 weight and you knew exactly what you were getting.

If you want a 100-weight fleece or a close approximation, which is usually quite sufficient for active hiking or snowshoeing, the inexpensive fleece pullovers or jackets from REI, Decathlon (size up), The North Face, and Lands End are often your best bet.  My goto fleece hoodies are made by Ragged Mountain Equipment in Glen, NH a few miles from my home. Go to the store for the best selection as their website sucks. They have really unique clothing. Fleece vests are also a great mid-layer because they are very effective at keeping your core warm, but your arms cooler, and they can be vented in front.

Wool mid-layers can also be suitable as mid-layers, including hoodies, although they wick and dry somewhat slower than their synthetic counterparts. I’ve had the most experience with wool pullovers and hoodies from Minus33 which is another New Hampshire brand, which my friend Wanda also likes. While they hang in my closet, they’re just too warm and heavy for me to wear often. Still, they may be a good option if you run cold.

Many hikers seem to think that insulated synthetic and down jackets make good mid-layer garments. While they are good passive layers to throw on if you take a break and want to ward off a chill, they make remarkably bad active mid-layers because you’ll be too warm if you try to hike in them, you’ll sweat like a pig, and soak your base layer and the jacket liner. You are much better off wearing cooler layers that will keep your baselayer and mid-layer insulation drier for the entire day. Winter hiking and snowshoeing generate a huge amount of body heat and you’re not going to be cold if you’re moving. But don’t take my word for it. Go try it. That’s how everyone learns what they prefer when it comes to layering winter hiking clothes.

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