The Best Long Underwear and Base Layer for Men

Ross Robinson hiking around the city of Arequipa in southern Peru  with the 6 000+ meter Chachani volcano in the background.
Long underwear options are seemingly overflowing from the shelves. With so many choices, we researched more than 80, picking 11 of the best to test side by side. For months in both South and North America, our experts lived and sweated in these layers, experiencing both warm and bitter cold temps. Over the course of the test, our team compiled detailed stats on each contender's warmth and breathability, putting them through soak tests and timing how long each took to dry. The experts also evaluated each piece's comfort and style, noting which pulled uncomfortably in certain areas and whether or not a piece was applicable for multiple uses. With all the data, we were able to narrow the playing field, providing you the info you'll need to purchase the right piece for you.

Read the full review below >

Test Results and Ratings

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Analysis and Award Winners


Review by:
Ross Robinson
Senior Review Editor
OutdoorGearLab

Last Updated:
Saturday
May 20, 2017

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Updated May 2017
Are your base layers getting stinky? Since it might be time to re-up, we updated this review as of May 2017, adding helpful comparison charts and graphs to aid you with your decision. We also analyzed the current market to ensure that our Editors' Choice winner still earns top honors.

Best Overall Pair of Long Underwear


SmartWool NTS Mid 250


SmartWool NTS Mid 250 Zip T Editors' Choice Award

Extremely comfortable
Warm for the weight
Stylish
Odor resistant
Breathable
Expensive
Limited durability
Dries relatively slowly
Throughout our many tests, a clear winner became obvious. Merino wool and more specifically the Smartwool NTS Mid 250, had significant advantages over competitors, making it a favorite and our Editors' Choice. Combining a stylish construction with craftsmanship that added comfort, it was a piece we could quickly forget we were wearing (in a good way). The slim-fit waist helped it stay in place during activity, and the wool's gentle stretch added to our ability to move unencumbered. In cold temps, the NTS was our first layer, and it worked well on its own in warmer conditions. While some contenders were better suited for a particular use, if we could only have one base layer, the NTS Mid 250 would be it.

Read full review: Smartwool NTS Mid 250

Best Bang for the Buck


The North Face Warm


The North Face Warm Best Buy Award

$59.95
at Backcountry
See It

Smooth comfort
Solid all around
Superior durability
Inexpensive
Snags easily
Not very warm
Average drying speed
Looking at some of the prices in the base layer marketplace, you might be wondering if it's possible to purchase an effective base layer that doesn't break the bank. The answer lies in The North Face Warm. From the moment we slipped into this smooth operator, we were impressed by its comfort. It doesn't itch but rather caresses your torso. It's capable when layering over and under this model, and it breathes sufficiently, too. We were psyched on this product's durability, with bomber seams and solid synthetic fabric. It didn't regulate temperature as well as some of the merino wool and blended fabric products, but we found it suitable to a range of activities and temperatures. For exceptional value in a base layer that is built to last several seasons, we recommend our Best Buy award winner, the Warm from The North Face.

Read full review: The North Face Warm

Top Pick for Lightweight


Rab Merino+ 160


Rab Merino+ 160 Top Pick Award

$109.95
at CampSaver
See It

Very breathable
Fastest drying model
Excellent comfort
Lightweight
Not very warm
Low durability
In our field of competitors, there wasn't a lightweight model that performed nearly as well as the Rab Merino+ 160, which only weighs 7.5 oz. This product of blended merino wool and polyester rocked the boat in several categories, giving new inspiration to what thinner, lighter base layers are capable of. It has an excellent fit, feels great, layers surprisingly well, and breathes like a mechanical lung. Most impressively, this was the fastest-drying fabric in the group of competitors. Being so thin, it didn't provide much durability or warmth. Our reviewers and friends also agreed that this model is good to go for social environments as well. However, if you're looking for the best combination of performance and low weight for use in mostly cool temperatures, or cold weather as a first layer, our Top Pick for Lightweight award winner offers just that.

Read full review: Rab Merino+ 160

select up to 5 products
Score Product Price Our Take
79
$100
Editors' Choice Award
The SmartWool deserves our Editors' Choice for providing excellent performance in almost every metric, making it an exceptional choice for a wide variety of activities and temperatures.
75
$110
Top Pick Award
Our Top Pick for Lightweight, the Rab Merino+ 160 is a champ of moderate temperatures, with an excellent fit and comfort, great breathability, and a fast drying fabric in a lightweight package.
74
$145
The Arc'teryx Rho AR is a great first or second layer in cold and frigid temperatures, as long as you avoid sweating while wearing it.
72
$90
The REI Merino Midweight provided above-average performance across the board without wowing us in any specific areas. It's all you need, without any extras.
70
$60
Best Buy Award
With a solid performance across the board, and stand-out comfort and durability, this relatively inexpensive contender presents a great value, and wins our Best Buy award.
68
$90
The Icebreaker Oasis is a solid merino wool base layer that has several nice features, but also fails to keep wrists and lower stomachs protected due to its short lengths.
66
$59
The Capilene Midweight is a strong choice for moderate to high intensity activities in cool weather, but isn't warm enough to be suited for the cold.
65
$90
We loved the tasc Base Layer for its ability to move along with our bodies across a wide range of activities, as well as its significant warmth and breathability, but were disappointed in its lack of durability.
61
$76
This contender is moderately priced for a merino wool, but a lackluster fit and overall underwhelming design didn't perform as well as its competitors in most metrics.
58
$85
The 4.0 is suited for traditional team sports in cold weather, but doesn't fit in with the rest of the crowd for most outdoor recreational activities.
57
$55
The Microchill 2.0 will keep you warm and last a long time, but its low performance against the skin in breathability, drying speed, and comfort make it better suited as a mid-layer.

Analysis and Test Results


A good layering system is required to be safe and comfortable in the outdoors, especially when conditions turn cold and/or wet. The foundation of the modern layering system is next-to-skin long underwear. This appropriately named 'base layer' has arguably the greatest impact on your comfort during active pursuits. It is the only piece that comes in direct contact with the vast majority of your upper body skin. Small defects in design, like chafing stitches or an improper fit, can become frustrating agonies during extended use.

All the models in our review are seen here  hanging during our speed drying test. The manufacturers  from left to right: Mountain Hardwear  Arc'teryx  Minus33  Under Armour  REI  SmartWool  The North Face  Icebreaker  tasc  Rab  Patagonia.
All the models in our review are seen here, hanging during our speed drying test. The manufacturers, from left to right: Mountain Hardwear, Arc'teryx, Minus33, Under Armour, REI, SmartWool, The North Face, Icebreaker, tasc, Rab, Patagonia.

Maintain some perspective, however, as a quality base layer needs to be more than just comfortable when you're active in the outdoors. An itchy fabric might be annoying, but a product that collects moisture and doesn't keep you warm when wet can potentially be life-threatening. It is for this reason that cotton has almost disappeared from technical outdoor apparel. Sure, cotton is comfortable, but once this fabric becomes saturated, it cannot provide any insulation. A wet and cool situation can quickly lead to hypothermia, or worse. From this you should see that the selection of appropriate long underwear is more important than it may initially seem; both for your happiness and health.

Layering up with the Base 4.0 from Under Armour. The mid-layer pictured here is the Patagonia R1 Hoody  which won the Top Pick in our review of fleece jackets.
Layering up with the Base 4.0 from Under Armour. The mid-layer pictured here is the Patagonia R1 Hoody, which won the Top Pick in our review of fleece jackets.

To learn more about proper layering systems for outdoor activities, reference our three part layering systems article.

This review focuses on base layer models designed for three-season use during periods of inactivity to moderate physical engagement. Our selection includes products typically considered to be lightweight or midweight base layers. For lighter shirts that will work for running and other warm activities, consider running shirts. Thicker insulating options are examined in The Best Fleece Jacket for Men Review.

This product from Rab was excellent for hiking with a pack up and down in Colca Canyon in southern Peru  where temperatures fluctuated often from 50 to 70 degrees Fahrenheit throughout the day.
This product from Rab was excellent for hiking with a pack up and down in Colca Canyon in southern Peru, where temperatures fluctuated often from 50 to 70 degrees Fahrenheit throughout the day.

Types of Base Layers



Wool, Synthetics, and Blends


The most popular base layers today largely fall into three categories: wool, synthetic, or a blend of the two. Each offers their own set of advantages and disadvantages. Typically, wool in the premium long underwear marketplace means merino wool, which is made from a special breed of sheep with finer fibers that make it softer than the scratchy sweaters of old. One of our favorite features of merino wool is its ability to regulate the microclimate between skin and shirt.

We found that it tends to perform great across a wide range of temperatures. It also breathes well (dry or wet), resists absorption of water, and dries quickly. Some adrenaline junkies (we won't point any fingers) might benefit most from its natural anti-odor properties. It is, however, expensive, delicate, and an allergy to some. The 100% merino wool products we tested in this review are the SmartWool NTS Mid 250, REI Merino Midweight, Icebreaker Oasis, and Minus33 Isolation Midweight Wool.

The merino wool fabric products  from left to right (and lightest to heaviest): Icebreaker Oasis  REI Merino Midweight  SmartWool NTS Mid 250  Minus33 Isolation Midweight Wool.
The merino wool fabric products, from left to right (and lightest to heaviest): Icebreaker Oasis, REI Merino Midweight, SmartWool NTS Mid 250, Minus33 Isolation Midweight Wool.

The synthetic garments currently available are primarily composed of polyester, which is sometimes combined with a secondary material (spandex, elastane, etc.) to add specific design properties, like elasticity or warmth. Synthetics tend to cost less and last longer, qualities we certainly admire. They also don't itch as much as wool garments, which is especially important to anyone with sensitive skin. On the flip-side, though, these fabrics offer lower performance in temperature regulation and breathability, and can work up a ripe smell during active use. The strictly synthetic models in this review are The North Face Warm, Arc'teryx Rho AR, Patagonia Capilene Midweight, Mountain Hardwear Microchill 2.0, and Under Armour Base 4.0

The synthetic fabric products  from left to right (and lightest to heaviest): Patagonia Capilene Midweight  The North Face Warm  Under Armour Base 4.0  Arc'teryx Rho AR  Mountain Hardwear Microchill 2.0.
The synthetic fabric products, from left to right (and lightest to heaviest): Patagonia Capilene Midweight, The North Face Warm, Under Armour Base 4.0, Arc'teryx Rho AR, Mountain Hardwear Microchill 2.0.

Hybrids are, like, the future, right? As you might expect, fabrics created from a blend of wool and synthetic materials attempt to connect the best of both worlds. These products aim for higher warmth to weight ratios, better breathability, and more odor-resistance than synthetics, but also increased durability and comfort over wool products (although this was not the case in our experience). The two blended fabric models featured in this review, the tasc Base Layer and Rab Merino+ 160 were just as expensive as the merino wool products.

The blended fabric products  with the lighter Rab Merino+ 160 on the left and the tasc Base Layer on the right.
The blended fabric products, with the lighter Rab Merino+ 160 on the left and the tasc Base Layer on the right.

The world's most popular fabric, cotton, will not insulate when wet and can actually draw heat away from the body. This is what makes it so nice to wear in hot and humid climates, but also means it is inappropriate for use in the variable conditions found away from central heating. The prices are usually tempting, but taking cotton into an active outdoor setting is ill-advised and potentially dangerous.

Thick vs. Thin


Base layers are also diverse in their range of fabric thickness, which can greatly influence a top's performance regardless of the material. In theory and in general practice, thicker fabrics tend to provide greater insulation and higher durability. On the other hand, we experienced increased breathability and drying speeds in the products with thinner fabrics. When choosing a product in this category, we consider fabric material to be of utmost importance, followed closely by the thickness of the fabric.

Reviewer Ross Robinson ready for flight with the three lightest base layer tops in this review; the Icebreaker Oasis  Rab Merino+  and Patagonia Capilene Midweight.
Reviewer Ross Robinson ready for flight with the three lightest base layer tops in this review; the Icebreaker Oasis, Rab Merino+, and Patagonia Capilene Midweight.

Design Type


From top to bottom: the Microchill 2.0  the Warm  and the Rho AR. We generally favored the versatility provided by zip-neck tops.
From top to bottom: the Microchill 2.0, the Warm, and the Rho AR. We generally favored the versatility provided by zip-neck tops.
The two most common base layer top designs are crew cut and zip-neck, with turtleneck, hooded, or full-zip options also scattered throughout the market. With the exception of the Arc'teryx, Minus33, and Under Armour models, the models we tested are available in multiple design options. Our reviewers generally prefer zip-neck base layers, as they offer greater versatility through manual ventilation, plus a higher collar for when the mercury drops. However, uncomfortable zippers can be less pleasant under other layers than crew cuts, and a broken zipper can swiftly eliminate all the benefits of a zip-neck.

There are several factors that go into a quality base layer. In this review  we attempted to accurately quantify their importance in our weighted system of metrics.
There are several factors that go into a quality base layer. In this review, we attempted to accurately quantify their importance in our weighted system of metrics.

Criteria for Evaluation


Through extensive research and consideration of our own experience wearing base layers, we created six separate metrics for scoring each product — warmth, breathability, comfort and fit, drying speed, durability, and layering ability. We also assigned different scoring weights to each metric based on their importance for this type of product. When deciding which base layer to get, consider your own intended uses, as well as your body type. Reference the chart below to learn where each base layer ranked in overall score.


Warmth


Warmth is an important consideration when selecting long underwear, but it should not be the only factor. After all, if warmth were all that mattered, we would all be sweltering in down filled, one-piece jumpsuits. Rather, warmth must be combined with breathability to create an effective layer that can be worn comfortably when active or at rest. The fit of the product can also have a large influence the insulation it provides, with baggy or short fits being less effective than more snug, longer cuts. Consider these variables when selecting the best shirt for your intended use. High exertion activities or warmer temperatures may be better enjoyed in a lower warmth scoring product. Just like Goldilocks' porridge, long underwear should not be too hot, or too cold, but just right.


For our purposes, warmth was measured without consideration for weight. Each piece was rated according to the insulation they provide relative to the other products in this review. Generally, wool layers were warmer for their weight than their synthetic counterparts. Wool also regulated our body temperature the best when actively used in a wider variety of temperatures, keeping us from overheating or freezing in warm and very cold environments, respectively. The Editors' Choice award winner SmartWool NTS Mid 250 was especially impressive when active in high and low temperatures. As none of these products contain any cotton, they will maintain their insulating properties when wet.

Ross Robinson in the Rho AR from Arc'teryx  heading up the iconic El Misti shield volcano in Arequipa  Peru. The below-freezing temperatures required a warm top like this one  but we were somewhat disappointed in its breathability when we began to sweat.
Ross Robinson in the Rho AR from Arc'teryx, heading up the iconic El Misti shield volcano in Arequipa, Peru. The below-freezing temperatures required a warm top like this one, but we were somewhat disappointed in its breathability when we began to sweat.

Other factors affected the scoring in this metric, too. The tasc Base Layer features a very long torso, extending down 13 inches past the top of our main reviewer's hips. This model, as well as the Arc'teryx Rho AR, also had extra long sleeves which kept our wrist from exposure to cold air at all times. Several base layers in this review were also designed with an extended length on the backside of the shirt (often referred to in the industry as a drop tail). Who doesn't appreciate some extra warmth and care for their derrière?

In the zip-neck models, we liked the products that included an extra strip of material behind the zipper to block chilling winds from entering through here, as seen on the Rab Merino+ 160. We also liked the thumb holes and loops, found on the tasc, Patagonia Capilene, and Under Armour Base 4.0, which increased the material coverage of the tops up to our knuckles, without the dexterity loss that comes with gloves.

A behind the "seams" look at various designs. From left to right and from most to least protection against air passage through the porous zipper area  the Merino+ 160  NTS Mid 250  Merino Midweight  and Rho AR.
A behind the "seams" look at various designs. From left to right and from most to least protection against air passage through the porous zipper area, the Merino+ 160, NTS Mid 250, Merino Midweight, and Rho AR.

Breathability


Breathability is the yin to warmth's yang. While lying on the couch, warm and cozy clothing is the bomb. But when on the move, your body starts to warm up, and that heat needs to escape, or you will be trapped in a nightmare of sweat. Enter breathability and the 2nd law of thermodynamics! Breathability is the ability of a material (in this case, fabric) to allow moisture to pass through it, made possible by the natural movement of hot and moist air between your skin and the inside of your shirt to an area of cooler, dryer air outside your shirt.


Thus, a breathable shirt will allow the moist air produced from perspiration to escape through the material and into the outside environment without saturating the fabric. A non-breathable shirt will prevent the moisture from escaping, causing it to condense on the inside of the garment. A non-breathable base layer would be miserably sweaty, and therefore dangerous in cold conditions.

A highly breathable base layer  like the tasc model  is enough to make our reviewers dance and shout. Even the best base layer won't improve your moves  though. Sorry.
A highly breathable base layer, like the tasc model, is enough to make our reviewers dance and shout. Even the best base layer won't improve your moves, though. Sorry.

It should be noted that during periods of high physical activity, the rate of transmission of moisture through any fabric is likely too slow to prevent condensation on the inside of a garment. Yet, upon reducing or ceasing this activity, the moisture should quickly escape through the fabric on products with good breathability.

The products we tested all breathe well, especially when compared to the laminated fabrics of waterproof shells, where this property is much more important and variable. Additionally, keep in mind that because these tops are so breathable, they will not offer any protection from wind. For blustery conditions, they will have to be paired with a hardshell or softshell or one of the ultra-light, nylon, wind breakers that are beginning to gain popularity.

After removing the pack from his back on a hike along the coast of California  moisture poured out of the Capilene Midweight  which is so breathable  we could sometimes see it!
After removing the pack from his back on a hike along the coast of California, moisture poured out of the Capilene Midweight, which is so breathable, we could sometimes see it!

In addition to our breathability assessment throughout months of use hiking, skiing, climbing, and more in the backcountry, we also designed a test to learn more about each top's capability in this category. One at a time and in a temperature-controlled, indoor environment, we worked up a sweat with the same short but rigorous exercise routine, consisting of pull-ups, push-ups, mountain climbers, burpees and jump squats, while wearing each base layer. We then timed how long it took for our skin and the inside of our shirts to dry after stopping. Performing the worst in this test were, unsurprisingly, the three heaviest models we tested, the Minus33, Arc'teryx Rho, and Mountain Hardwear Microchill.

Working up a sweat with an indoor workout to test breathability in the Base 4.0.
Working up a sweat with an indoor workout to test breathability in the Base 4.0.

The tasc Base Layer and Under Armour 4.0 both scored the highest in this category. Tight, thin products stretch the fabric out against the skin, increasing the air space between fibers and allowing more water vapor to pass through. The merino wool options also performed well and took longer to absorb moisture or feel wet than the synthetics of comparable thickness.

Comfort and Fit


A base layer's comfort and fit should probably be the most important selection factor, as it can affect the top's performance in nearly every other metric. However, this is also the most subjective category to evaluate. For this review, we tried to consult with testers from a range of body types and interests to fairly assess what is often a personal opinion.


If possible, we recommend heading to the fitting room of an outdoor retailer in your neck of the woods. Different body shapes and personal preferences can affect a product's comfort and fit.

We took several factors into consideration to determine the comfort and fit score for each product. We noted each material's softness and comfort next to skin, and judged areas of the top that were too loose, too tight, or just right. We checked for mobility, performing calisthenics like jumping jacks and windmills to look for any limitations. We really paid attention to the potential for the sleeves to slide up the arm when moving around, which we found to be an annoyance. We liked even less models that exposed our vulnerable bellies when our arms were raised. Other details, such as the type of sewing technique on the seams and the potential to build up static electricity weighed in on the scoring.

This year's Editors' Choice award winner is the most comfortable and best fitting model we reviewed  and sufficiently breathable as well.
This year's Editors' Choice award winner is the most comfortable and best fitting model we reviewed, and sufficiently breathable as well.

The types of fabrics play a significant role in each product's comfort. While merino wool is very soft, it can also be itchy. Everyone seems to have a different tolerance for the itchiness of wool, but for those allergic to this material, it can be an awful wearing experience. Shirts with blended fabrics can make you scratch and adjust, too; the tasc Base Layer was the most itchy, despite consisting of only 30% merino wool. The SmartWool model was the least itchy of the merinos, and the softest. Stealing the show with next to skin comfort was the Best Buy award winner, The North Face Warm.

In terms of fit, we like shirts that had slim-fitting waists, which prevented the bottom of the shirt from raising up and baring our stomachs when reaching overhead. Similarly, products like the Arc'teryx Rho AR had extra long and snug sleeves, which resisted sliding up our forearms. The Icebreaker Oasis was very comfortable, but we were frequently annoyed with our stomachs and wrists constantly being exposure when moving around, especially when climbing. Our favorite fitting shirts were ones that didn't squeeze too tight in the chest and neck, nor fit too baggy over our torso and arms. The right snugness allowed some models to move and flex with our bodies, without needing constant re-adjustment.

Monkeying around the Santa Monica beach in the very flexible tasc model. This product was great at staying in place during dynamic body movements.
Monkeying around the Santa Monica beach in the very flexible tasc model. This product was great at staying in place during dynamic body movements.

Inspecting the seams, we were pleased that almost all models featured flatlock seams, with the exception of some seams on the Mountain Hardwear Microchill 2.0. Flatlock seams, as their name implies, lie flat, which we found to minimize/eliminate chaffing, especially when layering or actively wearing these products. Also to our delight, almost every product was void of seams top and center on the shoulders, which would have been uncomfortable under backpack straps. Again, the Microchill 2.0 was the only exception. Several models did have underarm gussets implemented in the sewing design. These increase mobility and create less strain on the materials at high flex-points. The North Face Warm was the only model to also include gussets on the side /and/ bottom of the shirt.

In the end, we were able to sort out some winners and losers. We deemed the overall softness, mobility, and fit of the SmartWool NTS Mid 250 enough to qualify it as top dog in this category. The Arc'teryx Rho was the comfiest synthetic model, and the Rab Merino+ 160 top was our favorite blended fabric in terms of comfort. Scoring the worst in this category was the Under Armour Base 4.0, which squeezed way too much for our liking. It felt like someone had a choker hold on our neck while pinching our armpits at the same time. The Mountain Hardwear Microchill 2.0 also failed to impress in this category, with a scratchy logo on the inside, stiff neck, and very loose fit.

The discreet inner flatlock seam of the SmartWool on the left  compared to the more irritating overlock seam of the Mountain Hardwear on the right.
The discreet inner flatlock seam of the SmartWool on the left, compared to the more irritating overlock seam of the Mountain Hardwear on the right.

Drying Speed


Getting wet in the outdoors is unavoidable. Whether it is from precipitation outside or sweat from within, your long underwear will eventually get wet, and when it does, the time that it takes to dry can have a significant impact on your comfort and warmth. Many of these products advertise proprietary technologies that speed drying, like the waffled Polartec® Power Dry® fabric of the Patagonia Capilene Midweight, or the Moisture Transport System on Under Armor Base 4.0. To cut through the baloney, we conducted an air dry test to measure each shirt's time to dry in a controlled setting.


This experiment was straightforward: we got all the tops completely soaked, hung them up, and timed how long it took them to dry. It was as boring as it sounds. The times we measured were not important in absolute terms. Your shirts will not be drying at the same temperature or humidity and probably will have a warm body to assist the process. Rather, it was the performance of each shirt relative to the others that was significant.

The waffled cells of these two products (Patagonia on the left  Under Armour on the right) helped increase their breathability and drying speed simultaneously.
The waffled cells of these two products (Patagonia on the left, Under Armour on the right) helped increase their breathability and drying speed simultaneously.

For this reason, in our reviews we have changed the time in hours we recorded to a percentage comparable to the best finisher. We think this is more fair and useful. Keep in mind, though, that some of the tight fitting tops, like the Under Armour 4.0 and tasc Base Layer, might have performed even better with the fabric stretched over a body, creating more space for air to pass between fibers, instead of simply being hung on a hanger.

From that experiment, we came to one conclusion that now seems logical and obvious; thin fabrics dry faster than thicker fabrics. The Rab Merino+ 160 was the winner in this test, and also happened to be one of the least dense layers. Across all of the layers tested, thickness was a better predictor of performance than material or advertised features. This should be an important (and common sense) consideration for retail shoppers, heavy sweaters, and outdoor enthusiasts who seem plagued by rain clouds overhead.

Soaking all the products for our drying speed test. Some of the models were resistant to becoming saturated until we agitated them under a constant stream of water.
Soaking all the products for our drying speed test. Some of the models were resistant to becoming saturated until we agitated them under a constant stream of water.

Our air dry test also corroborated merino wool manufacturers' claims that wool can absorb up to 30% of its own weight in moisture before feeling wet to the touch. Before starting the test, each of the shirts had to get soaked. The merino wool layers resisted, and had to be physically agitated underwater before they would become fully saturated. The synthetic Arc'teryx Rho and Mountain Hardwear Microchill 2.0 also did a fair job in resisting water absorption. The North Face Warm and Patagonia Capilene Midweight models slurped up the water like a thirsty dog. We took these factors into consideration as well when scoring for this metric.

Durability


The high cost of some of these pieces makes durability an important consideration. We inspected the strength of the fabrics and quality of seams and stitching to come up with the score in this metric. We also looked for signs of damage at the end of our testing period, and detracted points in this metric for obvious pilling of the fabric. Overall, a higher durability rating for some of these tops generally coincided with a greater thickness.


All these products are made with quality in mind. When examined from a long term view, however, it becomes likely that the synthetic options will outlast their wool counterparts. One of the testers liked to joke that merino wool layers make great golf shirts because pretty soon they all have 18 holes. This is certainly an exaggeration, but we did find some truth at the heart of this statement. The explanation for this is that the greater warmth of wool for the weight allows it to be sewn into a thinner garment than a comparably warm synthetic; predictably, durability suffers.

A close-up of some differences in seam construction. From left to right  the Capilene Midweight  NTS Mid 250  Merino+ 160  Merino Midweight  and Base 4.0.
A close-up of some differences in seam construction. From left to right, the Capilene Midweight, NTS Mid 250, Merino+ 160, Merino Midweight, and Base 4.0.

Another drawback of wool is the potential for shrinkage if laundered incorrectly, but if you don't toss it in the dryer on high, then this is not a concern. Conversely, wool is more durable in the sense that it doesn't absorb unpleasant odors. Therefore, it shouldn't have to be washed as often. The synthetic options all scored well on durability; so you can wash the stench they attract off without fear of wearing through the fabric. This longevity adds to their already superior value.

Some wool products claim to be safe for the dryer on the low tumble dry setting. However, we find flat-drying these products to be the best practice to increase longevity.

The Mountain Hardwear Microchill 2.0 model struck us as the most durable product in this review. After months of extensive use, it didn't let lose a single thread, or show any signs of wear at all. Its thick material should hold up for seasons to come, too. The REI Merino Midweight impressed us with its quality, compact seam design.

Somewhat to our surprise, the blended fabric models in this review fared the worst in this metric. The base layer from tasc had the most battle scars at the end of our testing period, with holes on one sleeve, a tear in its thumb loop, and several areas of the stitching coming loose. The hemming on the Rab Merino+ 160's sleeves and shirt bottom was coming undone in multiple areas, and its thin fabric looked susceptible to damage in the near future.

The Mountain Hardwear product is probably the most durable model we reviewed this year. Its seams are strong  as well as its fabric  making it ready for rugged backcountry use. The footwear in this photo are the Arc'teryx Bora2 Mid boots  featured in our latest hiking boots review.
The Mountain Hardwear product is probably the most durable model we reviewed this year. Its seams are strong, as well as its fabric, making it ready for rugged backcountry use. The footwear in this photo are the Arc'teryx Bora2 Mid boots, featured in our latest hiking boots review.

Layering Ability


All of these tops can function well as a next-to-skin layer in the right conditions, and some can also be worn over other garments should the situation warrant this. We tested each model for its layering ability by trying each one on over a tight-fitting t-shirt, as well as a tight-fitting long sleeve base layer. Then, we tested each model's fit and mobility under moderately tight-fitting jackets and mid-layers to discover the total range in layering ability. While performing these tests, we were on the look-out for fabric bunching up (especially in the armpits), the product's ability to stay in place under another layer, and any restrictions in mobility.


The thick, snug, and very stretchy Arc'teryx Rho AR was the best in this category. It stretched easily over other layers, but also hugged our bodies underneath mid-layers without affecting mobility. The Mountain Hardwear Microchill 2.0 was loose enough to fit over t-shirts and other base layers, but was too baggy to fit nicely under mid-layers. Our main reviewer actually preferred to use this product as a mid-layer with another shirt next-to-skin. Almost all these models perform acceptably over another layer. The Under Armour Base 4.0 was the exception. Its form fit prevents it from being comfortable on top of anything else. This category did not impact the overall review too much because it is not a true requirement for a base layer. Therefore, it only accounted for 10% of the overall score.

Ross Robinson utilizing a three layer system while skiing in the Sierras. As a base is the Under Armour model  with the SmartWool playing the part of mid-layer  and a Basin and Range hardshell as the outer.
Ross Robinson utilizing a three layer system while skiing in the Sierras. As a base is the Under Armour model, with the SmartWool playing the part of mid-layer, and a Basin and Range hardshell as the outer.

Best for Specific Applications


Wool Allergy: Anyone who is physically bothered by the itchiness of merino wool should first consider The North Face Warm or Patagonia Capilene Midweight.

Team Sports: Traditional sports athletes competing in cold weather will probably appreciate the breathability and stretch of the form-fitting Under Armour Base 4.0.

Casual around Town and Aesthetic Style: We think the Rab Merino+ 160 is the best-looking model included in this review, complete with its lighter-colored seams serving as stylish accents. We think our Editors' Choice award winner, the Smartwool NTS Mid is pretty good-looking, too.

Conclusion


Our Best Buy award winner from The North Face proved its value with its great comfort  durability  and all-around solid performance.
Our Best Buy award winner from The North Face proved its value with its great comfort, durability, and all-around solid performance.

Quality long underwear products should score well across most, if not all, of these metrics. They need to keep you warm and dry, wicking away the sweat of fear, be compatible with other layers, and remain cozy and comfy while engaging in physical activity or lazing about the house - all while looking good. As usual with recreational gear and equipment, we highly recommend you consider your intended uses and environments before snatching up your first/next base layer. We hope we've been able to help you narrow down your choices to a few best matches. If you're still unsure about which of the many market options will be most appropriate for your needs, read over our Buying Advice for some guidelines and tips to narrow it down even further.
Ross Robinson

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