There’s no such thing as bad weather, only bad clothes.
I’m a cold-hater. I’ve always had a hard time trying to acclimate to colder climates, and not just because I come from a place where the mercury never dips below 20°C. Friends, family, and people I shake hands with tend to get a shock from by my frigid fingers!
In my perpetual quest to find better base layers that can help extend my endurance to cold during my adventures, I’ve accumulated several different brands of women’s base layers (or “thermal underwear”). I’ve tested most of these in -10°C to 10°C temperatures, through strong winds and snow, doing everything from hiking to waiting – for hours on end – to capture the perfect photos.
So which brands make the best base layers for women? Read on for my opinion.
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Review: the best natural base layers
Think of base layers and merino wool instantly pops into mind. Merino base layers are immensely popular due to their natural warmth, wicking ability, and softness (no wool itch!) However, after traveling to Mongolia where the extreme cold is tempered with clothes made from fur, cashmere, yak, and more, I became curious about other natural textiles like yak wool and alpaca fleece. Here’s what I found:
Kora (yak wool)
I was seriously excited when I discovered Kora. This small company specializes in high-performance yak wool technical clothing that is supposedly warmer, softer, and more breathable than merino. (If you’re skeptical, as I tend to be, check out studies like this and this.)
What I like about Kora is their claim that their yak wool is ethically sourced from Tibetan nomadic herders, meaning your purchase of Kora clothing supports these local communities. Watch this video to see how yak wool is collected!
Of course, all this means that Kora’s gear doesn’t come cheap. Their Shola 230 tops and leggings (100% yak wool at 230gsm) cost 2-3 times as much as those from Icebreaker and other natural base layers. That said, they’re really well made. If you spend vast amounts of time outdoors in extreme cold, Kora base layers are worth the investment.
Reduced heat loss compared to merino wool or synthetic base layers
Great design and luxurious feel
100% yak wool is water repellent (merino is hydrophilic)
Extremely expensive – double the average price of merino base layers
Arms of Andes (alpaca fiber)
Arms of Andes is a small company I discovered in my search for alpaca base layers. Despite being new to the outdoor wear market, this Peruvian company is extremely knowledgeable about working with alpaca – they’re involved in every step of the production process, from sourcing cruelty-free Royal alpaca fiber from local co-ops to weaving, sewing, and shipping each piece.
At 18 microns, Royal alpaca is finer than merino wool (19 microns) and other types of alpaca fiber, making it super soft. While Arms of Andes only has 230gsm midweight base layers and mid layers for now, they’ll be releasing shirts, leggings, and sports bras in 2019.
100% Royal alpaca, slightly finer than merino
Water repellent (merino is hydrophilic)
Fit is for the more shapely
Limited color, cut, and weight options
Woop!Wear (alpaca fiber)
Just like yaks, alpacas live at much higher altitudes than merino sheep, and thus have much warmer coats to help them endure the harsher cold. Alpaca fibers are also said to be softer than merino, but they lose their shape more easily over time – that’s why Woop!Wear uses a blend of alpaca and Tencel to help add elasticity.
Woop!Wear only offers a simple crew neck base layer in limited colors for both men and women. However, their prices are very affordable compared to merino base layers, so I recommend trying them out.
Cheaper than merino base layers
Quality blend of alpaca and Tencel (natural fiber, odor-resistant like cotton)
Limited color, cut, and weight options
Icebreaker (merino wool)
Think merino wool base layers and usually, Icebreaker is the first brand to pop into mind. They’ve created a great, reliable product for outdoor enthusiasts, and I like that their base layer tops come in multiple collar styles. Icebreaker also has expedition weight (400) base layers in addition to the popular midweight (200gsm) pieces.
While some Icebreaker base layers can be found on Amazon, I recommend checking outdoor retailers like Moosejaw and Backcountry.com as they have a wider selection and often have discounts on Icebreaker clothes.
Established, trusted brand with multiple weights, colors, and styles
Sometimes has issues with stretching and wearing out
Minus33 (merino wool)
After the closure of Ibex, another leading maker of merino wool base layers, people began hunting for alternatives – and Minus33 was one of the few that rose to prominence. The company focuses solely on merino wool garments,
I personally prefer Minus33 to Icebreaker, especially when it comes to the little details: the Women’s Sequoia Midweight 1/4 Zip has a chin guard, while the Icebreaker Oasis (nor Smartwool and Woolx) doesn’t. However, the leggings in particular seem to stretch and get holes in them more quickly.
Soft and warm with attention to detail
Crew and zip neck available, tops come in several colors
Sometimes has issues with stretching and wearing out
Paradox (merino blend)
In my research, I also came across merino blend base layers. Merino blend thermals supposedly combine the best of both worlds, giving you the softness and warmth of merino wool as well as the elasticity and quick-dry properties of synthetics. Yet, they’re not commonly sold.
Paradox is the only brand I’ve found with substantial reviews so far, as it initially retailed in Costco. Although the Paradox merino blend base layers only comprise 11% merino wool, it’s got glowing reviews from users who claim that these are indeed odor-resistant and sufficiently warm.
Given how subjective “warm” is and how susceptible I am to cold, I’m not inclined to gamble on these as I’m happy with my GearX synthetic base layers (read on to see what I’m talking about!)
Supposedly as odor-resistant as pure merino base layers
More for lounging/light winters than outdoor activity
Review: the best synthetic base layers
Synthetic base layers often get a bad rep for stinking up fast and feeling clammy on the skin, but they’re great starters for those who are unfamiliar with the cold (like me) or don’t travel all that often. Synthetic base layers also dry quickly after washing for quick turnaround on trips. Here’s what I’ve tried:
Since its expansion beyond Europe, Decathlon has quickly become known for selling quality sporting gear at delightfully low prices. When they opened in Singapore I got my hands on their Simple Warm Base Layer, which at $6 is easily the cheapest base layer you can buy.
The Simple Warm Base Layer has a brushed inner and stand-up collar meant to help keep you warm. However, the 100% polyester fabric quickly proved fatal when I went hiking in Seoraksan and started working up a sweat. Within hours I was stinking and felt suffocated, even with just a t-shirt on top. The collar seam was also itchy, and the inside of the fabric pilled severely after just one wash.
While they’re warm, I simply wouldn’t recommend Decathlon for anything other than sedentary walking/lounging in cold places. You may have better luck with the other base layers in their range if they’re not 100% polyester.
Fits reasonably well and keeps you warm
Stinks to high heaven in no time
Itchy and irritating seams
Poor moisture wicking
Korean brand GearX hasn’t done much marketing, but they’re the best synthetic base layers I’ve owned to date. I actually purchased their Hard Winter tops and leggings from Gmarket, but some of their products are can be found on Amazon.
The Hard Winter base layers feature flatlock seams and a micro-brushed lining, while the entire garment is buttery soft. I’ve never really believed in the efficacy of antibacterial treatments, but the GearX base layers stayed impressively dry and stink-free through 2-3 intense days of hiking and driving on my Canadian Rockies road trip!
Although I found them really comfortable to wear – snug but breathable without that clingy plastic feel – they’re cut to Asian sizes and have limited stretch. Try going a size up if you’re between sizes; I promise they’re worth a shot.
Silky soft, great quality, and cheap
Wicks moisture well with virtually no odor (antibacterial treatment)
UPF 50+ sun protection
Runs small; size chart in product images is more accurate. (I’m a US size 6 and wear M for these)
Comes only in black or white
Under Armour’s ColdGear base layers have a huge fan following, and their expansion beyond the US has now made the brand bigger than ever. Yet, they’ve stuck to purely functional designs in their ColdGear and UA Base series of thermals (though I can’t really tell the difference in features from their website’s product listings).
Unfortunately, my UA ColdGear top is slightly loose and I wish I’d sized down. Also, given the $50-$80 price tag, it seems to make more sense to get a wool base layer instead.
Uniqlo claims its Heattech technology somehow “converts moisture into warmth” with ultra-fine microfibers. People on Reddit and hiking/backpacking forums have also praised these base layers for their exceptional lightweight warmth. Me? Not so much.
I’ve used Heattech and the upgraded Heattech Extra Warm (with brushed lining) on several trips, and each time I had to wear double layers just to be able to tolerate the cold. I haven’t tried the latest Heattech Ultra Warm series (all this marketing is getting ridiculous IMO), but Heattech base layers are definitely comfy and don’t stink too badly. I’d say it’s good for 5-10°C temperatures if you get cold easily, like I do.
Very soft, stretchy, and comfortable
Lots of colors and neckline options
More for casual urban travelers than serious outdoor activity
Thin fabric doesn’t attenuate the “skin chill” of evaporation
Base layers or thermals aren’t meant to keep you warm. At least, not in the way a thick insulating fleece or down jacket would. However, base layers are the foundation of the layering system one should employ when dressing for wintry weather. This is what you should consider when choosing a base layer:
Scientifically speaking, warmth is a relative measure: we all know a tepid 25°C glass of water will feel warm in 10°C weather and refreshingly cool on a 40°C day. Therefore, when comparing base layers, the fairest way of comparing “warmth” is how well it retains body heat, especially via evaporation.
A good base layer material will wick sweat away from the surface of your skin, rather than a) having the sweat evaporate from your skin and causing chill, or b) absorbing the sweat and eventually becoming damp and cold. To learn more, check out this in-depth guide on different base layer materials by Montbell.
Fit and durability
In order to effectively retain body heat and wick perspiration as described above, your base layers should fit snugly to the body. No matter how good a base layer is, it won’t work if it’s too loose as it leaves a layer of air between your skin and the base layer.
If you get warm and remove your outer layers, your base layers may experience wear against your backpack, trees and rocks, and so on. 100% merino wool base layers are known to be less durable and acquire holes more quickly, so consider if blends or synthetics may be more suitable for your planned activities.
As you remain toasty warm in your layers of insulating winter clothing, your base layer is the one getting the most heat and perspiration – so the last thing you want is to come indoors and take off your jacket only to smell like a swamp!
This may not be mentioned much in many base layer guides, but weight is the key difference between technical base layers and traditional thermal underwear. Have you ever wondered how women in frigid winter cities like Seoul manage to go out with just a fashionable pair of tights? It’s because those are ultra-cozy fleece-lined tights.
Toasty warm as they may be, fleece-lined garments like these (and even the heavyweight wool base layers) are much heavier and bulkier when you want to travel light. They function more like insulating mid-layers – check out this detailed guide on base layer weights by Eastern Mountain Sports.
Conclusion: the best base layers for women
For now, my favorite natural base layers for cold weather are from Minus33, which offer a great balance between quality and price. I’m still stocking up on GearX synthetic base layers though, as they’re just so incredibly cheap, light, and comfortable for anywhere above 0°C.