Ever been deluged with positive messages about Merino wool? I have been. My friends, neighbors, professional associates, and a slew of catalogs, advertisements, and websites all toll the virtues of Merino wool and its ability to keep us warm.
If it’s this good, I thought, why do we still use other materials for our outdoor wear? Why aren’t all of us snowshoers wearing it for all three layers plus our headgear, gloves, and footgear?
I got curious enough to investigate outdoor-fabric products, customer experiences of these products, and the science of staying warm while active outdoors in the winter. No doubt I’ll help stir up more debates than I help resolve, but here’s what I found.
The Truth to Layering
Before we jump into the Merino wool’s impact on keeping us warm, there are a few layering aspects to clarify.
First, the three layers we all hear about – base, insulating, and shell – are based on sound science.
We need a base layer to move sweat away from our skin. We need an insulating layer to trap heat in the air space around our body (and keep our sweat moving out). And we need a shell layer to protect our body from the snow, wind, and cold air and allow our sweat to evaporate.
Second, in all three layers, whether we get lightweight, midweight, or heavyweight (expedition weight), clothing can make a big difference.
Lightweight is for high-energy activity on a mild day. Midweight is for moderate-energy activity on a moderately cold day. And heavyweight – or expedition weight – is for a frigid day in the mountains when it’s below zero.
Merino Wool for a Base Layer
Based on the truths of layering, it is tough to refute that Merino wool makes the best base layer.
Our base layer – the clothing next to our skin – is all about sweat management. Sweating cools our skin, our circulatory system, and our body. Sweat sucks heat away from our body 25 times faster than does the air; wet skin cools 25 times faster than dry skin. When our skin is humid, our body senses heat, and we sweat even more.
To keep our skin dry, we need a base layer that wicks – that draws sweat away from our body, spreading it through the fabric. Without wicking, our thermal insulation drops 30 percent to 50 percent.
The Pros as a Base
Overall, the science is clear: wool is number one for wicking.
Wool is tough, quiet, anti-bacterial and anti-microbial, biodegradable, and flame-retardant. So we can sit by our fireplace or campfire in our wool-long johns without worrying whether a spark will set them ablaze. And wool’s so elastic it retains its shape; you can bend a wool fiber 20,000 times without breaking it.
Technically, wool is fabric from sheep, goats, llamas, alpacas, yaks, and similar animals. If you can afford cashmere, mohair, or Alpaca wool long johns, go for it. Otherwise, Merino wool is the best of the sheep wools.
Next to our skin, Merino wool is soft, stretchy, supple, and comfy. It’s finer and lighter, it’s even better at wicking sweat away from our skin, and it’s more odor-resistant. In addition, Merino wool stays warm when moist or damp, protects us across a range of weather conditions and helps provide our body with excellent temperature regulation.
The Cons as a Base
Wool has three disadvantages: It costs a bit more than synthetics. We can’t dry it in a machine; it shrinks. And it takes longer to dry than synthetics; when it gets soaked, we may need to wring it out.
Comparisons to Synthetics
A moisture-wicking fabric is a highly absorbing fabric. Cotton makes us colder. Silk is expensive and not very durable, and wet silk sucks the heat out of us. Down is almost perfect, except that it’s super-pricey and can never get wet.
But, what about synthetics like polypro and polyester? Synthetics wick away sweat, are lightweight, keep us warm when wet, and dry fast. But synthetics are also noisy, clammy and sticky, and highly flammable. They absorb the short-chain fatty acids that cause body odor. So, they may become foul-smelling after just one day. It seems no matter how many times you wash them, that they may still stink. And for some people, polypro is also scratchy; you don’t want it next to your skin.
However, as synthetics evolve more, include scent eliminators that you might allow next to your skin. For example, X-Static technology (now Ionic+) uses positively charged ions to eliminate microbes and, thus, odor. Acrylic long johns, Cupro fabric, and the synthetic down called Polyguard can provide three other alternatives.
Here are a few examples of companies producing Merino wool base layers and a few current options, including long legs, three-quarter legs, and one-piece base layers.
Smartwool – Men’s & Women’s Midweight Merino 250 Bottoms
Ibex – Men’s & Women’s Merino Wool Woolie Bottoms
Icebreaker – Men’s & Women’s Merino 200 Oasis Leggings
Ridge Merino – Women’s Aspect Merino Wool High Neck Top.
Patagonia – Men’s & Women’s Capilene Midweight Bottoms
Bambool Thermics (Merino wool combined with Bamboo fibers) – Men’s Baselayer Top
Merino Wool for a Mid-Layer
Merino wool is as good for our insulating layer as any other material on the market.
The slower our heat energy transfers away from the body, the warmer we stay. Like a sleeping bag, our insulating layer traps in our body heat as it traps in the air around our body. Our body protects us from cold with its own heat, as long as we keep that heat near us. Our insulating layer locks in place the air that our body heats while keeping our sweat moving away from our body.
The best insulating layers are vests and sweaters made of fleece and other polyesters and polyester blends (including pile), acrylic and other polymers, wool, and cashmere. For most of us, the choice comes down to wool or fleece.
Polyester fleeces are light, more affordable than wool, dry much faster than wool, and are water-repellant, but they degrade in harsher environments (and can be torn up by thorns). In addition, fleece is flammable; it is risky to wear it near a fireplace or campfire. Again, they may also be noisy and stinky, although antimicrobial treatment can help maintain the garment’s freshness.
Wool retains 60 percent of its insulating qualities when wet, making it a better insulator when wet than polyester. Thus, Merino wool does keep us warm as a mid-layer. Also, wool is more wind-resistant than synthetics. And wool is more durable. Wool’s downside is that it both costs more and weighs more.
Many companies with good reputations offer mid-layer attire that can insulate us well. Among the unique mid-layer wool attire are the following:
Merino Wool for an Outer Layer
Merino wool coat or jacket makes little sense as our shell layer.
What we need is a hard-shell jacket that is water-repellant (preferably water-proof) and wind-resistant, and largely wind-proof, with some “breathability.” We want a robust and durable shell – a non-insulated jacket – that will keep snow, cold air, and wind out of our base layer and insulating layer. Wool simply doesn’t measure up to the alternatives for our outer layer.
Read More: Jacket Reviews
Merino Wool for Accessories
Merino wool seems to be a very good choice for headgear, gloves, and socks.
A wool hat or balaclava, layered socks, and layered gloves and mittens can keep us a lot warmer than accessories with lesser fabrics. Woolen mittens from Dachstein, Austria, are favored by many winter adventurers.
For ten thousand years, human beings have met the challenges of winter with clothing made from sheep’s wool. For six thousand years, human beings have walked the Earth on snowshoes. And since the late 1990s, the winter outdoor sports have been in the throes of what some observers call a Merino wool renaissance.
Today, we can build on all of this experience with both snowshoeing and wool to keep ourselves warmer than ever during each of our snowshoeing experiences.
What are your thoughts about whether Merino wool can keep you warm? What are some of your favorite Merino wool base and mid-layers? Please share your insights with us in the comments below.
This article was first published on November 10, 2014, and was most recently updated on Dec 12, 2021.