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I contributed a comparative review of the best base layers for winter trail running to "RUN+TRAIL Vol. 23" published by Sanei Shobo and released on February 27th!
Most of the gear introduction articles I have contributed so far have been re-edited versions of content that was originally published on the site, but this time, as part of a collaboration between RUN+TRAIL and Outdoor Gearzine, I have written original reviews that have been comparatively evaluated as part of a magazine project over the past month
This issue introduces, from a user's perspective, how to wisely choose key items for trail running, from choosing shoes that everyone is interested in, to backpacks and base layers. There is also a wealth of other interesting content, including a multifaceted article on the current state of the activity of trail running. Be sure to pick up a copy
As mentioned above, Outdoor Gearzine was in charge of providing impressions of winter base layers. We picked out a wide variety of models in terms of material, form, and functionality, and compared and reviewed them. This time, we'd like to present an article that was originally published in a magazine, with additional information added for the website. Here you go
table of contents
table of contents
- About the items tested this time
- Test Results & Spec Comparison Table
- Individual Impressions
- Actual driving impressions [Overall review]
The best part of trail running is being able to freely enjoy the charms of nature, which changes with the seasons. There are sure to be many runners who look forward to the quiet winter fields once the season has died down
Choosing the right clothing is more important than ever to safely enjoy winter trail running. The basic concept is the same as for mountain climbing and other outdoor activities: layering, which involves wearing multiple layers of clothing with different functions to address the multiple challenges of blocking out the cold outside air while quickly releasing large amounts of sweat from the body
Among these layers, base layers, which are clothing that comes into close contact with the skin, are a direct cause of accidents such as hypothermia, so it is no exaggeration to say that they are the key to winter layering. In this article, we will compare base layers, a key layer when choosing winter clothing, from various manufacturers' models, from the perspective of use on trail runs
About the base layers we compared this time
Needless to say, the most important thing to be careful of during this season is how to deal with the cold. When outdoors in winter, even more so than in summer, you need to protect yourself from getting wet and the cold air, or your life could be in immediate danger. For this reason, unlike in autumn, when sweat absorption and quick-drying were the priority, winter base layers require a reasonable level of warmth. However, unlike mountain climbing, trail running, which requires constant, intense movement, and excessive warmth can easily lead to discomfort when moving around. In that sense, it can be said that compared to models designed for serious mountain climbing, more sweat absorption and quick-drying properties, as well as mobility such as a good fit and ease of movement, are required
Base layers have evolved remarkably over the past few years. We've seen advances in materials like merino wool, synthetic fibers, and blends of these, as well as various technological innovations like unique stitching and added functionality. For this review, we selected six distinctive models, carefully choosing them to test out as many variations as possible in terms of material, stitching, thickness, and form. While some models ultimately received favorable reviews, our goal was simply to identify styles that are easy to use. Therefore, please don't take the conclusions of this review at face value; instead, make your own final decision based on the evaluation
The try-ons were carried out in January and February on roads in Tokyo and on trails around Tokyo, where temperatures were around 0 to 10 degrees Celsius, together with Kohei Tsushima, who also writes for the site
Test Results & Spec Comparison Table
| Overall ranking | 1st place | 2nd place | 3rd place | 4th place | 5th place | 6th place |
|---|---|---|---|---|---|---|
| item |  |
 |
 |
 |
 |
 |
| Overall score (out of 100) | 83 | 82 | 81 | 77 | 76 | 75 |
| Reference price | 11,880 yen | 17,280 yen | 11,880 yen | 15,120 yen | 10,800 yen | 3,498 yen |
| Here is ◎ |
Warmth, comfort, fit, functionality |
Comfort |
Warmth, fit |
fit |
Sweat-wicking, weight |
Weight, moisture wicking, price |
| Here is △ |
weight |
Nothing in particular |
Sweat-wicking, weight |
Sweat-wicking |
Warmth, fit |
Comfort, fit |
| Heat retention (25 points) |
21 | 20 | 22 | 18 | 15 | 16 |
| Sweat-wicking (25 points) |
20 | 20 | 18 | 18 | 24 | 22 |
| Comfort (20 points) |
18 | 19 | 17 | 15 | 14 | 13 |
| Fit (20 points) |
17 | 15 | 17 | 18 | 14 | 14 |
| Weight (10 points) |
7 | 8 | 7 | 8 | 9 | 10 |
| Specifications | ||||||
| item | Smartwool PhD Light Zip Tee | Patagonia Capilene Air Crew | Icebreaker Oasis Long Sleeve Half Zip | Rab Merino Plus 160 Long-Sleeve Crew | Arc'teryx Phase AR Crew LS | Mont-bell Geoline LW Round Neck |
| Actual weight | 217g(S) | 160g(S) | 217g(S) | 171g(S) | 148g(S) | 133g(L) |
| material | 56% wool, 44% polyester |
51% wool, 44% polyester (Capilene) |
100% wool | Wool 63% Polyester (37.5) 37% |
100% polyester (phasic) | Polyester (Zeoline) 100% |
Reference: Fit image of each model
Individual Impressions
Smartwool PhD Light Zip Tee
Achieve everything you need for winter running at a high level
Mesh under the arms improves breathability and thumb holes increase the warmth of the extremities, making it even more comfortable in the middle of winter
The PhD series is a particularly technical category in the Smartwool lineup, designed to deliver high performance in more demanding activities. As the title suggests, it was packed with features that made it perfect for winter trail runs like this one, and I was able to experience the quality that exceeded my expectations
The fine, supple texture of the high-quality wool and the soft, mellow seams make it comfortable to wear. While the semi-form fit, which isn't too tight around the body, may not be enough for some, the carefully mapped pattern ensures no excess slack even during intense movement. At 210g/m², it's not the lightest among the garments reviewed here, but it's certainly one of the warmest. Compared to other models, it lost significantly less body heat when exposed to wind, not just under normal conditions. While this might raise concerns about its sweat management capabilities, the unique wool-polyester blend absorbs, wicks, and releases moisture well. Additionally, mesh under the armpits minimized stuffiness and the feeling of wet clothing clinging to the body, though not to the point of being dry
A word from Tsushima: This is a jacket packed with useful features for winter. It will be especially effective in situations with large temperature differences, such as during an all-day run
Patagonia Capilene Air Crew
The unique wool blend material provides exceptional comfort that will have you hooked
The seamless, direct knitting construction ensures a comfortable feel against the skin and minimizes waste during production
Patagonia's latest base layer features an intriguing texture never before seen, and is an ambitious product made with their proprietary "Merino Air" fabric, which is made by knitting a blend of ultra-fine merino wool and synthetic yarns in a zigzag pattern with grooves
First and foremost, it's incredibly comfortable. The loft and grooves created by the unique stitching make it light, soft, and comfortable against the skin. It fits gently, snuggling up to your body. And the warmth created by the layer of air close to body temperature that forms between the fabric and your skin envelops you from the moment you put it on. What's more, this layer also keeps wet clothing away from your skin while you're running, reducing the uncomfortable feeling of tightness
However, one thing that bothered me a little was that it's so breathable that you can't expect much warmth from it if you're exposed to the elements without layering properly. Personally, I found the fit a little loose for running wear, which left me feeling unsatisfied. In that sense, perhaps its best use is mountain climbing or skiing in the depths of winter, but overall, it's definitely an appealing piece of clothing that can be used for a wide range of activities, from everyday wear to extreme activities, depending on how you use it
A word from Tsushima: This is quite comfortable on its own, but once it gets wet it loses comfort drastically, so it's best used in situations where you're not pushing yourself too hard
Icebreaker Oasis Long Sleeve Half Zip
100% merino wool for superior warmth and a slim fit
The deep half-zip at the neck makes it easy to adjust the temperature inside the garment, a great feature for trail running
One of the features that makes merino wool superior to other fibers is its temperature and moisture control capabilities. It retains heat when it's cold and releases moisture from sweat when it's hot, always maintaining an optimal temperature and humidity level inside clothing. The Oasis series, a staple of Icebreaker, one of the top brands in the North American merino wool apparel market, is made from 100% top-quality New Zealand merino wool, and this was a garment that allowed me to fully experience its charm
First and foremost, the extremely smooth feel and the tight, taut body shape not only provide functionality but also stimulate aesthetic sensibilities. However, since it's not particularly stretchy, some people may find it a little tight, so be sure to try it on first. The fabric weight of 200g/m² is just the right thickness for cold seasons. As expected, the heat retention is excellent, with body heat being transferred to the fabric from the moment I put it on, and I felt warm throughout the entire garment, even after sweating
However, it's important to note that these fabrics don't necessarily dry quickly, so even if you have sweat remaining on them, you won't feel uncomfortable. Some people can't get used to the unique moist feeling and prefer the dry, smooth feel of 100% synthetic fabrics, so they might not be suitable for them
A word from Tsushima: It's easy to regulate the temperature and highly versatile. You won't feel cold even when it's wet, so it's perfect for long runs, especially long distances
Rab MERINO + 160 LS Crew
The calculated fit and quick-drying properties make it ideal for intense winter activities
The raglan sleeves reduce stress on the shoulders during exercise, and the sides are stitched to prevent tension, ensuring a comfortable fit
The latest merino wool model from a British brand dedicated to creating products that can withstand demanding activities in the world's most challenging places
Not just for base layers, but I'm always impressed by Rab's cutting techniques, which are always slim and stylish while also providing high mobility, and this model certainly lived up to my expectations. The calculated, stress-free fit is as expected. Of course, there is a good chance that individual body types will have different results, but personally, out of all the items I tried on this time, I felt that this model had the best balance of comfort and ease of movement
However, there are a few points of concern regarding the material. The unique wool and synthetic fiber blend uses "37.5 Technology," which attaches active particles of carbon with numerous pores to the surface of the fibers, making it easier to quickly absorb and evaporate sweat from the skin. However, during my test run, although the quick-drying properties were high, I found that the fabric did not stay on the skin as easily as other products once it became saturated with sweat, which was a concern compared to other products, and I was disappointed that I didn't feel as dry. Also, although the merino wool blend is a bit high at 63%, the light fiber weight of 160g/m², and the smooth texture and high breathability mean that I didn't feel as much warmth as I had hoped
A word from Tsushima: It's thin and stretchy, so it's perfect for when you want to pick up the pace. However, be aware that it doesn't have the best heat retention
Arc'teryx Phase AR Crew LS
Stay dry no matter how far you go with sweat-wicking, quick-drying performance
By using different functional fibers on the inside and outside in different configurations, we have achieved optimal absorbency, quick-drying properties, and a dry feeling on the skin
This season's updated Arc'teryx classic synthetic base layer is a high-tech model that uses the latest synthetic fibers to deliver excellent performance in stop-and-go activities. As always, the uncompromising spirit of exploration that brings these ideas to life is exciting
What really impressed me while running was how I never got wet, no matter how long I wore it. This extraordinary dryness was unmatched. The secret lies in the newly developed fabric material. Two different types of fibers have different properties: one is highly hydrophobic, providing a dry feel against the skin, while the other wicks moisture toward the surface, making it quick-drying. By weaving these two fibers in different proportions on the front and back of the fabric, the two layers' different roles of keeping the skin dry and wicking sweat away from the surface can be more efficiently performed
The only drawback is that the fabric is less stretchy than other models, making it difficult to fit depending on your body type. In my case, I couldn't get rid of the uncomfortable gaps around my shoulders and chest. I was also concerned about the poor heat retention, which is a common problem with 100% synthetic fibers. In winter, it's essential to layer up with a mid-layer or other suitable item
A word from Tsushima: The smooth fabric is easy to put on and take off, and it's also excellent at absorbing sweat and drying quickly. On the other hand, it may feel a little cold in the winter
Mont-bell Geoline LW Round Neck Shirt
Comfort, functionality, safety, and cost-effectiveness. Easy to use with all the essential features
It is so thin that you can see through it, providing high moisture absorption, quick drying, and a dry feeling, while still ensuring a minimum level of heat retention
It's a long-standing favorite among hikers due to its overwhelming cost performance. I actually considered a thicker model, but the shop assistant's confident words led me to choose this one
My first impression is that it's incredibly light, which is to be expected considering it's a model that can be used in the summer. At 133g for the L size, it's only about 100g lighter than the heaviest model here at 220g, but when I actually ran with them, the difference in comfort was clear. Made from 100% synthetic fiber, it boasts excellent sweat management and quick-drying performance. But what surprised me most was that, despite its lightness (thinness), it was surprisingly warmer than I expected in still wind. The fiber itself retains air, and the crimping makes it easy to create an insulating layer. And best of all, the ceramic incorporated into the fiber radiates heat, warming the body from the inside out, all thanks to an ingenious system that provides excellent warmth per weight
However, compared to other models, it has limitations in terms of heat retention, and it feels a bit rougher against the skin than merino wool. The short sleeves and loose fit around the sleeves and waist not only didn't suit my body type, but also felt a bit loose for running
A comment from Tsushima: "It's so thin and light that I was able to ride without any stress. It's perfect for when you're pushing yourself hard."
[For those seeking advanced comfort] Highly recommended high-performance mesh underwear
Did you know that in recent years, an item called "high-performance mesh underwear" that is worn underneath a base layer to significantly increase comfort has been gaining popularity?
These underwear have two major advantages. One is that their extremely high sweat-processing ability boosts the "sweat-wicking and quick-drying" function, one of the functions of a base layer. However, some people may think that this is no different from a thin mesh shirt for summer. Another major advantage that sets high-performance mesh underwear apart from these is that it significantly reduces the problem of "chilling from sweat," which is a problem with base layers
Generally, mesh fabrics are thought of as being "cool," but when you actually wear these models with a base layer and move around, you'll feel more than ever that they keep you warm even when you're sweating. For example, Millet's "Drynamic Mesh" absorbs moisture and quickly transfers it to the upper layer, while the mesh traps dead air, creating a layer of comfortable temperature close to body temperature to maintain warmth
Although each brand has a different approach, the common concept is that they dramatically improve comfort while on the move all year round by significantly reducing the discomfort of sweat and chill.If you want to push yourself harder or are looking for a higher level of comfort, we highly recommend giving them a try
If you are interested in more details about our high-performance mesh underwear, please refer to this special feature page .
Outdoor Gearzine's recommended high-performance mesh underwear: MILLET DRYNAMIC MESH series
Actual driving impressions [Overall review]
It is generally said that synthetic fibers are good at managing sweat and drying quickly, while natural fibers such as wool are good at retaining heat, but through trying on the jackets this time, I realized once again that each model has a wide range of performance that cannot be easily explained by such generalizations. For example, even with just one material, the properties can vary surprisingly depending on the composition and proportion of the blend, and even with the same merino wool, the properties can vary depending on the quality and stitching
With that in mind, what made the biggest impression on me was the overall ease of use of merino wool for winter activities. To comfortably run on a winter trail, high sweat processing ability, warmth that keeps you warm even as sweat evaporates, and a comfortable fit that minimizes stress are all essential elements. In that sense, merino wool doesn't excel in any one aspect, but it has a good balance in all aspects, so it was impressive that it ended up being the most comfortable and easy to use
Among them, Smartwool was particularly well-received, taking advantage of the high heat retention of merino wool, which is so strong that it doesn't even bother with the wind, while also providing excellent comfort, fit, and sweat management, and it was also very well-balanced and high-level in all aspects, including the adjustable collar and sleeves.By the way, the zipper under the neck, thumbholes, and underarm mesh were more effective than expected in regulating temperature and providing effective ventilation, so it is a good idea to choose models with these features added, even from other brands
On the other hand, even models like Arc'teryx, which have outstanding sweat management capabilities, are of course not unsuitable, and it is quite possible that adding insulation and wind resistance through layering will make them more comfortable. The important thing is to understand the characteristics of each and use appropriate layering so that the whole piece works well. As long as you don't make any mistakes in that regard, all six models featured here will perform excellently
Finally, one thing we must remember from our two separate attempts at trying on and evaluating the garments is that the desired features and evaluations will vary slightly depending on the wearer's body type, level of competition, and preferences. In reality, it can be quite difficult to differentiate numerically in each category. I would like to add in closing that individual impressions and numbers are only for reference, and that what is ultimately important is the feeling you get when you actually wear the garment
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