The world's most in-depth and scientific reviews of outdoor gear

The Best Base Layers for Women of 2019

The Smartwool 1/4 zip is a little thinner allowing it to layer a little easier than others. Here we add another layer of warmth during this super cold day at Mt. Baker in Washington state.
By Amber King ⋅ Senior Review Editor
Friday November 8, 2019
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Are you a woman in search of your next great base layer top? We researched the best options on the market before settling on 10 promising models to test side-by-side. During our testing process, we stuffed these long underwear tops into backpacks, hiking, running, climbing, and exploring with each one. We've summited mountains, battled the North Sea on small sailboats, ski toured on snowy glaciers, and climbed to the tops of 1000-ft spires all across North America and beyond. With our expert experience and knowledge, we've been able to separate true award winners from mid-range performers, with our favorite recommendations highlighted for you.

Related: The Best Long Underwear Bottoms for Women


Top 10 Product Ratings

Displaying 1 - 5 of 10
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Awards Editors' Choice Award  Top Pick Award   
Price $78.99 at Backcountry
Compare at 3 sellers
$74.81 at Amazon
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$125.00 at REI
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$110.00 at Backcountry
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$104.98 at Backcountry
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Pros Wide range of thermoregulation, cute, super cozy, great fit, fantastic breathability, no odorGreat thermoregulation, exceptional at wicking, impressive durability, least itch factor of all wool tops testedCozy fleece interior, easy to layer, warm, high quality performance, versatile, stash pocket, tight fitGreat thermoregulation, comfortable and fitted fabrics, great patterns and colorsImmensely comfortable, quick to dry, lightweight, huge range of thermoregulation, no smell
Cons Lacks durability, absorbs waterNot very cozyMore expensive, not super breathablePoor durabilityLacks durability, expensive, harder to layer
Bottom Line Our favorite base layer with the best thermoregulation that we continue to love.Icebreaker uses the most comfortable wool in this seemingly lightweight base layer.This high performance synthetic is a Top Pick for pretty much any adventure you dream up.A great thermoregulator with some durability issues.An amazing balance of breathability and warmth with some layering issues.
Rating Categories Merino 250 1/4 Zip Merino 200 Oasis Crewe Rho LT Zip 185 Rock'N'Wool Long Sleeve Capilene Air Crew
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Specs Merino 250 1/4 Zip Merino 200 Oasis... Rho LT Zip 185 Rock'N'Wool... Capilene Air Crew
Fabric Weight Midweight (250-grams) Midweight (200-grams) Lightweight (185-grams) Midweight (185-grams) Midweight (147-grams)
Material 100% Merino wool 100% Merino Torrent (84% polyester / 16% elastane) 100% merino wool 51% merino wool/49% recycled polyester seamless zigzag knit comprised of 18.5-micron-gauge lofted wool
Cuts avaliable 1/4 zip, crew, 1/2 zip hoody Crew, 1/2 zip neck 1/4 zip neck Crew, 1/4 zip Crew, hoody
Smelly over time? No No Yes No No
Odor Control Fabric Naturally odor resistant Naturally odor resistant Polygiene Naturally odor resistant Naturally odor resistant
Thumb Loops? No No No No No
UPF (Sun Protection) 50 No N/A No No
Length (short, medium, long) Medium Medium Long Medium Medium
Fit (Based on 5'7, 140-lb woman wearing size small) Fitted (not tight), true to fit. Fitted (not tight), true to fit. Tight and long, true to fit. Fitted (not tight), true to fit. Fitted (not tight), true to fit.
Accessory Pocket? No No Yes (on arm) No No
Flat-lock seams (prevents chaffing) Yes Yes Yes Yes Yes

Best Overall


Smartwool Merino 250 1/4 Zip - Women's


Editors' Choice Award

$78.99
(25% off)
at Backcountry
See It

84
OVERALL
SCORE
  • Warmth - 25% 9
  • Breathability - 25% 8
  • Comfort and Fit - 20% 10
  • Layering Ability - 20% 7
  • Durability - 10% 7
Materials 100% Merino Wool | Weight: 250-g midweight
Incredibly comfortable
Thermoregulation range
Great wicking power
Comfortable fabrics
Heavy when wet
Not super durable

Wear this super comfy midweight top from the trail to your bed! The Smartwool Merino 250 ¼ Zip wins our Editors' Choice Award for its fantastic comfort and versatility. Loaded with 100% natural Merino wool fibers, it provides one of the most extensive ranges of thermoregulation tested. It functions well as a long underwear top and a wear-alone top in temperatures ranging from the double negative digits to highs of 70 degrees Fahrenheit. It outperforms every other shirt in this review because of its ability to keep us dry and comfortable when conditions went from warm to cold and wet to dry. The fabric wicks away moisture, dries quickly when on, and doesn't stink.

While the fabric is soft and cozy, the only thing that it truly lacks is durability against abrasive activities (we're yet to find a merino wool top that does). Also, when it gets wet, it absorbs quite a bit of water due to its thicker fabric. Then again, it can still insulate your body when soaked. Aside from these minor caveats, it performs wonderfully in all conditions and will keep you warm and comfortable out in the wild.

Read review: Smartwool Merino 250 1/4 Zip - Women's

Best Bang for the Buck


Patagonia Capilene Midweight Crew - Women's


Best Buy Award

$29.50
(50% off)
at Patagonia
See It

77
OVERALL
SCORE
  • Warmth - 25% 6
  • Breathability - 25% 9
  • Comfort and Fit - 20% 8
  • Layering Ability - 20% 7
  • Durability - 10% 9
Materials: 100% recycled polyester | Weight: 147-g midweight
Affordable
Easy to layer
Relaxed fit
Small wind barrier
Durable
Not as soft or warm as wool options

If the price is your biggest concern, focus your attention on this beautiful 100% polyester base layer top. Designed to wick away moisture and dry quickly, it offers great thermoregulation for even your sweatiest days. It offers a relaxed fit that flares out around the hips, accommodating all types of shapes. The smooth face fabric and nifty thumb loops also making layering underneath a fleece or any other layer super easy. Whether you're planning to wear it on its own or underneath another jacket, it offers many different patterns and colors to choose from, and the synthetic fibers offer more durability than merino options. Beauty and function all wrapped into one inexpensive package.

The downside? While there aren't many to this classic workhorse, the major difference we noticed between it and other merino base layers is its general feeling. When on, it feels comfortable, even when you sweat, it feels comfortable. However, because it integrates hollow fibers, cold air gets caught in them. So when you pull it on for the first time, it feels colder than other layers. However, once you start moving, it warms up with you. It's a relatively low-priced top that effectively moves moisture away from your body as you get after it out there. Nice.

Read review: Patagonia Capilene Midweight Crew - Women's

Top Pick for a Synthetic Option


Arc'teryx Rho LT Zip - Women's


80
OVERALL
SCORE
  • Warmth - 25% 7
  • Breathability - 25% 7
  • Comfort and Fit - 20% 8
  • Layering Ability - 20% 10
  • Durability - 10% 9
Materials: 84% polyester, 16% elastane | Weight: 185-g lightweight
Cozy and warm
Fitted design that's easy to layer
Longer fit through arms and torso
Stash pocket
Ultra-durable and well-crafted
Lacks some breathability
Expensive

After testing this piece for the last six years, it stands out as our go-to for all technical missions. The interior is fleece lined with wicking power that does a good job moving moisture. We love the fitted design that is stretchy and incredibly easy to layer, with a zip-neck fit for optional venting purposes. It's one of the most versatile base layer tops we've tested, performing well from ski tours in Colorado to mega rafting missions in the Grand Canyon. As is true with most synthetics, even after six years of hard wear, it shows minimal signs of durable. Tried, tested, and truly awesome.

This base layer doesn't offer the same level of breathability since the interior fleece layer that sits next to the skin can hold a little moisture when layered. Its high price isn't a huge plus either. However, given that this is one of the most time-tested pieces that we've had the opportunity of using, the value of performance you get out of it is definitely worth the price.

Read review: Arc'teryx Rho LT Zip - Women's

Top Pick for Lightweight Construction


Smartwool Merino 150 Crew - Women's


Top Pick Award

$59.99
(25% off)
at Backcountry
See It

73
OVERALL
SCORE
  • Warmth - 25% 5
  • Breathability - 25% 9
  • Comfort and Fit - 20% 6
  • Layering Ability - 20% 9
  • Durability - 10% 8
Materials: 87% Merino Wool, 13% Nylon Core | Weight: 150-g lightweight
Super breathable and lightweight
Great fit
Very layerable
Fabric knit is scratchy for some
Not warm, but that's not the point

Smartwool wins again with its lightweight base layer, the Merino 150 Crew. This long underwear top stands out for its ability to provide comfort during sweaty endeavors that might require a little extra wicking and drying powers. Thermoregulation is what this top is great at. Whether you're wearing it on its own during a snowy run, late Fall, or slipping it on for an uphill workout under a jacket, it moves moisture well without compromising comfort.

For those that are sensitive to wool (merino wool is renowned for its soft-to-the-touch feel that isn't itchy), it might feel a tad itchy. However, this is an observation only experienced by our testers that are super sensitive to wool fabrics. The majority of us didn't take notice of this point, and we thoroughly enjoyed pushing our aerobic limits in the cold with this top.

Read review: Smartwool Merino 150 Crew - Women's


Whether you're sea kayaking off the coast of Northern British Columbia or simply curling up next to a fire  a bomber base layer is at the core of your outdoor outfit. It'll keep you happy and safe for all types of adventures.
Whether you're sea kayaking off the coast of Northern British Columbia or simply curling up next to a fire, a bomber base layer is at the core of your outdoor outfit. It'll keep you happy and safe for all types of adventures.

Why You Should Trust Us


Out testing team is lead by Amber King. As a seasoned gear reviewer, she has worked with OutdoorGearLab for over six years, reviewing many different categories that reflect her tenacity and experience in the outdoors. She is a contracted outdoor education teacher that works with several school districts like Ridgway Schools to offer exceptional outdoor programming. She spends her time backpacking into remote places, canyoneering through slots deep in the earth, and finding cool trails to run around the world. Badass women she meets along her adventures become additional testers to provide unbiased, diverse, and genuine feedback on all base layer tops tested.

All of the base layers tested have been used for at least three months up to six or more years. When we go to make our selection, we take hours researching the best options on the market, then select the best ones to test against our award winners. Our testing involves wearing them everywhere we go. We've tested across the world, from the high glaciers of Alaska to the rainy and cool landscapes of Iceland. Trailrunning, backpacking, rafting, climbing, backcountry splitboarding, and hiking are just a few ways we've tested them. We take each layer on some bushwhacking hikes just to see how the fabric holds up when worn on its own. We also conduct objective tests to see how the fabric breathes and thermoregulates.

By wearing a base layer under a wind breaker  our main tester was comfortable and cozy while trail running over 100 miles in Peru. What do you demand from a great base layer top?
Alison layers her climbing pants overtop her baselayer while climbing on a cold day in Red Rocks. The abrasion of upper layers can cause holes to wear through if not careful. However  in the ultra-durable Patagonia Capilene Midweight  this didn't prove to be a problem.
Here we wear the Patagonia Capilene while skiing in Alaska. This base layer has provided great durability throughout the year.

Related: How We Tested Base Layer for Women

Analysis and Test Results


A base layer top is an integral part of any women's outdoor wardrobe. This piece sits closest to the skin, wicks away moisture, and ultimately keeps you warm and comfortable while tackling summits and lounging around the chalet. The base layer tops we chose are composed of either synthetic materials, merino wool, or a blend. No tops in this review contain cotton. Throughout testing, we rated each product using five key metrics: warmth, breathability, comfort & fit, layering ability, and durability. Our award winners either perform well in all or have a specialty for different uses.


Value


Wondering which top offers the best performance relative to its price? While the MSRP doesn't factor into our scoring metrics, we know just how important the performance received per dollar spent is. Typically, the largest trade-off in this category lies in the materials used. Merino wool tends to cost manufacturers more money than synthetic fabrics, and this higher price is passed on to the consumer. The two lowest-priced models in this review are synthetic tops. This includes our Patagonia Capilene Midweight, our Best buy winner and REI Midweight, which is also worthy of consideration. The REI option costs a little less than the Capilene, but it is at the price of performance and warmth. Both being crew tops, they cost less than zipping and hooded tops, so if you don't need those features, you can save some cash. Lastly, base layer tops often get color updates at least once a year. When that happens, it's a great time to snag the older colors at a friendly discount, making those pricey merino wool models more affordable.

A look at a few of the base layer tops we've tested.
A look at a few of the base layer tops we've tested.

Warmth


How many times have you started hiking, gotten your sweat on, then stopped only to shiver into movement once again? The tops that can keep you the warmest are those that will keep you warm while in action and while standing still. Different tops offer different weights of fabric and are rated based on this. High weight can be interpreted as thicker with more insulation. A heavy or expeditionary weight equates to more warmth while standing still and sitting around. The downside, however, is thicker fabrics typically hold more moisture than thinner ones, so they're not the best for activities where you might find yourself sweating. In general, if you know you're going to be sitting around in cold weather, choose a thicker option. If you think you're going to be moving a lot more with periodic breaks in cold weather, choose a thinner option.


During our testing, we only reviewed lightweight and midweight models. Keep in mind that most of the options listed here have different weight options. If you like the way a top sounds, check to see what other fabric weights it comes in.

When comparing fabrics, merino wool stands out as the best thermoregulator. When looking at comparative weights, it offers more insulating warmth and breathability, which equates to better thermoregulation overall. For example, the Smartwool Merino 250 1/4 Zip is the warmest and most insulating base layer in this review, packing in 250-grams of merino wool. The WoolX Hannah is just a little lighter (230-g), but on the trail feels like it delivers the same amount of warmth. Both kept us warm while running in the snow and skiing up mountains as an underlayer.

The Arc'teryx Rho LT offers stand-alone warmth with its cozy fleece-lined interior. Here we explore the stunning glaciers of Alaska on a 10-mile ski touring mission.
The Arc'teryx Rho LT offers stand-alone warmth with its cozy fleece-lined interior. Here we explore the stunning glaciers of Alaska on a 10-mile ski touring mission.

Some tops that are marketed as 'lightweight' actually feel more like a midweight and earned a high score as well. For example, the Icebreaker Oasis (200-g) and Ortovox Rock n' Wool (185-g) are both rated to a certain merino wool density. However, even the Rock n' Wool advertises a lower warmth rating, it feels warmer than the Oasis, which feels more like a lightweight base-layer given its thinner feeling design. Both offer great thermoregulation while testing on snowy trail runs and climbs in Red Rocks, Nevada.

All shirts did an excellent job at wicking away moisture for quick evaporation, except for the 240g Kari Traa Rose because of it's super tight-knit construction. Unlike the Arc'teryx Rho LT, which is constructed with a fleece layer to increase wicking capabilities (to keep moisture off the skin), the Traa Rose is too tight-knit. While its a very warm top (240 g, merino wool), it loses points simply because moisture would stay in the fabric. As soon as we slowed down after sweating, we would immediately feel cold.

Here we test the thermoregulation of the Smartwool 1/4 Zip which offers amazing warmth  even on this snowy day in the San Juans of Colorado.
Here we test the thermoregulation of the Smartwool 1/4 Zip which offers amazing warmth, even on this snowy day in the San Juans of Colorado.

The only merino-synthetic blend top that earns high points in this category is the Patagonia Capilene Air (147-g). Constructed of 51% merino wool and 49% recycled polyester, it provides a warmth that is almost as good as the Smartwool Merino 250 ¼ Zip. Whether you're sitting or running around, the fabrics wick amazingly well while the unique knit of the fabric holds warmth when it needs to.

While it is lightweight  the Patagonia 150 isn't the warmest when standing around. However  when running around in the woods during our first mountain snowfall  it proves to be a perfect base layer.
While it is lightweight, the Patagonia 150 isn't the warmest when standing around. However, when running around in the woods during our first mountain snowfall, it proves to be a perfect base layer.

Through our testing, most of the polyester tops we've tested don't offer the same 'sitting around' warmth as merino wool. Many are constructed with hollow-polyester fibers. When it's cold in the morning, and you pull the top on, it won't feel as cozy as a merino wool option simply because all the cold air is locked inside the fibers, cooling you down as well. However, when you start to move around, the top heats up with you. When moving from warm to cold, these tops typically adapt to their environment more readily than Merino wool. If you're wearing a polyester layer alone, while running or hiking, going from hot to cold, you'll also notice a drop in body temperature as well.

While this trend is true for most synthetic tops, some keep warm better than others. The Arc'teryx Rho LT is our favorite synthetic because it integrates a fleece lining, which increases wicking power and provides a thermal barrier between the skin and the shirt. No other base layer top provides this level of warmth and comfort in the realm of synthetic construction.

The first snowfall of the season! The Patagonia Capilene keeps us super dry and warm while on the go.
The first snowfall of the season! The Patagonia Capilene keeps us super dry and warm while on the go.

The Patagonia Capilene Midweight Crew offers more warmth than the REI Co-op Midweight simply because of the thickness and construction of the fabric. While the Co-op provides ample airflow, the fabric feels cooler on the skin than the Capilene. Both offer great drying speeds, though, so if you find yourself in a warm environment, you can take off your top, and it'll be dry in seconds, ultimately keeping you warmer and more comfortable.

The Smartwool 250 Zip continues to crush the competition. It does exactly what a good base layer should. Keeps you cool when you're hot and warm when you're cool. A perfect layer for any adventure  even cozy cabin ones.
The Smartwool 250 Zip continues to crush the competition. It does exactly what a good base layer should. Keeps you cool when you're hot and warm when you're cool. A perfect layer for any adventure, even cozy cabin ones.

Breathability


The yang to warmth's ying. Without great breathability, you're not going to have great warmth while playing in cool weather. A key metric for thermoregulation, this defines how well the fabric allows heat to escape in addition to its venting capabilities. When worn in a layered system, breathability enables fabrics to move moisture from the skin and through the fabric to the next layer.


Choose lightweight fabric for any of the tops we reviewed if you want something that'll breathe easier. Short-sleeve options are also available, as are zip necks that offer more ventilation. If you run hot, a lightweight fabric is the way to go, but if you get cold easily, opt for a midweight.

Here we take a training winter run after work with the Smartwool 1/4 Zip in a layered system. After the run where we transitioned from hot to cold  we felt comfortable. This Merino wool competitor thermoregulates well!
Here we take a training winter run after work with the Smartwool 1/4 Zip in a layered system. After the run where we transitioned from hot to cold, we felt comfortable. This Merino wool competitor thermoregulates well!

The best breathers are those constructed with thinner materials and fabric knit that isn't too tight to allow moisture to escape. Our favorite lightweight top is the Smartwool Merino 150 Crew. It offers a super-thin fabric design that offloads heat to keep you cool while you skin uphill. Unlike the Patagonia Capilene Air Crew that has a loose weave for optimal moisture off-load, 150 crew has a tighter knit. The Capilene Air, on the other hand, is a little thicker. Both are high scorers in this category and the best breathing tops.

The Patagonia Capilene Air is amazingly breathable  keeping its user warm while offloading excess heat quickly.
The Patagonia Capilene Air is amazingly breathable, keeping its user warm while offloading excess heat quickly.

The 100% synthetic construction of the Patagonia Midweight Capilene is also quite breathable. Its diamond-grid architecture promotes great airflow with a face fabric that cuts the win when worn on its own. The REI Midweight (synthetic as well) also offers great airflow, but while hiking and skiing, we noticed that it helped more moisture in its fabric than the Capilene. Another reason why the Capilene wins our Best Buy Award, even though Co-op is more affordable.

If you haven't noticed  we like to run...a lot. The Smartwool 150 offers exceptional breathability  earning a Top Pick.
If you haven't noticed, we like to run...a lot. The Smartwool 150 offers exceptional breathability, earning a Top Pick.

The Smartwool Merino 250 ¼ Zip, Icebreaker Oasis, and Ortovox Rock n' Wool all offer the same level of performance here. The Merino 250 has a loosely knit fabric design but thicker fabrics than either the Oasis or Rock n' Wool. The Oasis feels thinner than the Rock n' Wool but has a tighter knit construction. All three of these options breathe well, but when put underneath a non-breathable layer, they all absorbed a little moisture, unlike the Capilene and Merino 150.

Hiking uphill in Leavenworth  WA had us pushing the limits of breathability. One of the many ways we test our base layers.
Hiking uphill in Leavenworth, WA had us pushing the limits of breathability. One of the many ways we test our base layers.

Comfort & Fit


Ah, comfort…it's the little things that count. What's better than wrapping yourself in fabrics that are as soft and smooth as Cashmere for everything from on the trail to at-home comfort? When testing this metric, we assessed each top to determine which had the coziest fabrics and the most versatile fit. In most cases, this testing was the easiest - lazing about watching movies, hanging out around the campfire, going out with friends, and seeing how fabrics feel after day four of constant wear with no wash. In general, we love Merino wool tops with a fitted, stretchy design simply because they offer comfort both while playing and sitting at home. These, you can truly go from the hills to your bed without taking it off.


The truly cozy and cuddle-worthy Smartwool 250 Zip is the most comfortable fabric in this review. It features 250g of natural 100% New Zealand merino wool, a bit of stretch, and thicker cuffs and hemlines. It feels glorious against the skin with no itch and simply sheer comfort. We also love the Patagonia Capilene Air that hosts a gauntlet of comforts, but the neckline is a little high, and the fabrics aren't quite as cozy on the skin.

If you aren't prepared to buy it  don't try on the Capilene Air. It's very difficult to remove due to its happy-cozy-feels.
If you aren't prepared to buy it, don't try on the Capilene Air. It's very difficult to remove due to its happy-cozy-feels.

We also love the Ortovox Rock n' Wool. It offers a fitted yet comfortable shape with fabrics that feel thin and insulate well. We commonly wore this while running snowy roads in late Fall. Upon coming home, there was no need to take it off as the fabric doesn't retain smells, and the fabric feels so good on the skin.

The Ortovox Rock n' Wool offers a super comfortable and lightweight fit that we all love.
The Ortovox Rock n' Wool offers a super comfortable and lightweight fit that we all love.

The Icebreaker Oasis 200 and Arc'teryx Rho LT are also seriously cozy. While the Oasis 200 is a little thinner than the Rock n' Wool with a tighter knit fabric, it is not as cozy on the skin. However, we do love that the Rho LT has a fleece liner on the inside of the shift that feels amazing. Unfortunately, while you can wear the Oasis from the trail into the house, we found ourselves wanting to peel off the Rho simply because the synthetic fabrics can feel a little cold after cooling down.

Fit

When looking at fit, we handed these shirts to a group of women that varied in height, weight, and body shape. Some were tall while others were short, some had lots of curves, while others had none. In our evaluations, tops that had a stretchier and more voluminous fit proved to be the most versatile. We also looked at the relative lengths of the arms and torso to see which provided the best overall coverage. Our lead tester (5'7", 145 lbs) prefers size Small in most of these tops, but found the Kari Traa Rose, Ortovox 185 Rock 'N' Wool, and Icebreaker Oasis to fit better in size Medium.

A look at the length of the Hannah  a great Merino wool option for those with longer arms and/or torso.
A look at the length of the Hannah, a great Merino wool option for those with longer arms and/or torso.

Long Arms and Torso?
Need a shirt with long arms and torso? Luckily we have a host of options. Of synthetic tops, the Arc'teryx Rho LT has super stretchy fabrics that provide a next to the skin fit. The length of both the torso and arms are of some of the longest tested, working for both short and tall ladies, with and without a bust.

Layering Ability


A good base-layer can easily be worn next to the skin while layering a mid-layer or jacket overtop. While most long-underwear tops are presumably the "next-to-skin" layer, it is a bonus when you can wear a tank or tee underneath if you expect conditions to warm up. Not only that, but you want to make sure that you can throw layers on top and remove them without too much effort or static electricity that might cause your shirt to ride up. Here, we evaluated the knit of the fabric and spent time trying them on with different layers. Long underwear tops that did best in this category feature slippery face fabrics, a thinner construction, and thumb loops.


Synthetic layers typically have more rigid fibers that, in combination, make for easy layering. The Arc'teryx RHO LT proves to be the easiest to layer! The frictionless face fabric slides smoothly against even the fleeciest mid-layers like the Patagonia R1. The arms are long and can be held when layering to avoid frustrating layering situations like those experienced with more friction competitors like the WoolX Hannah that get stuck and roll up the arms.

Chopping down trees and gathering wood on a cold day in Ontario. The breathable Patagonia Capilene Midweight offers exceptional thermoregulation and layers easily under our fleece jacket.
Chopping down trees and gathering wood on a cold day in Ontario. The breathable Patagonia Capilene Midweight offers exceptional thermoregulation and layers easily under our fleece jacket.

The Patagonia Capilene Midweight is another great layering option with built-in thumb loops that keeps the arms in place while the REI Co-op Midweight has frictionless face fabric and super stretchy design that hugs the body. All are great options in this category.

Every model  especially the Arc'teryx Rho LT fits fine under a spacious jacket.
Every model, especially the Arc'teryx Rho LT fits fine under a spacious jacket.

Of the merino wool competitors, thinner options like the Smartwool 150, Oasis 200, and Ortovox Rock n' Wool are much easier to layer than thicker options like the Smartwool 250. The Kari Traa Rose works well because of its super tight-knit weave and skin-tight fit that makes sliding layers overtop easy. For all the layers mentioned above, look for ones with longer arms so you can grab the cuff of the fabric while pulling on a mid-layer that might be more grabby.

Layering the Hannah is a little harder than other synthetic competitors because of its stickier face fabrics. That said  we enjoy the long arms that allow us to pull them through the mid layer.
Layering the Hannah is a little harder than other synthetic competitors because of its stickier face fabrics. That said, we enjoy the long arms that allow us to pull them through the mid layer.

Durability


The best base layers out there should last you, although this category is notorious for not doing so. It shouldn't shrink, stretch out, pill, or fall apart after just a few months of use. Most importantly, a durable top shouldn't see holes after just a few times out on the trail. During our testing period, we shimmied through canyons and bushwhacked through forests to see if the fabric snagged or tore. We wore each with loaded backpacks. After all of this, we inspect each product to evaluate the craftsmanship. We inspect for holes, look for fly-away threads, and observe whether fabrics retain a sour stench over time. In general, we notice that synthetic competitors are far more durable, but struggle with retaining sticky smells and stains. Merino wool tops might not last as long, but they also don't let body odor linger in their fabric.


It's been six years since we started testing the Arc'teryx Rho LT Zip, and it's still going strong. Arc'teryx is known for its bomber craftsmanship, and this product is no different. We have used and abused it while climbing, hiking, split-boarding, and canyoneering. After many long years of use, there are still no signs of fly-aways or significant areas of wear and tear. Our only caveat is that the fabric retains a little smell with some pit stains in sweaty areas. However, this is easily abolished by a tech-fabric cleaner every month or so.

The Arc'teryx Rho LT is renowned for its craftsmanship and wonderful performance that has lasted us over six years and counting!
The Arc'teryx Rho LT is renowned for its craftsmanship and wonderful performance that has lasted us over six years and counting!

The Patagonia Capilene Midweight is also a workhorse. The synthetic fibers are strong and retain shape, even after a few years of testing. It's no wonder it offers the best value of tops tested. The REI Co-op Midweight is also fairly durable, but the fabric is thin and pills easily after just a few washes. However, after two years of testing, it is still functional, minus some undone stitches here and there.

Testing base layers under our fleece layers at Red Rocks while climbing several pitches of sandstone deliciousness.
Testing base layers under our fleece layers at Red Rocks while climbing several pitches of sandstone deliciousness.

Merino Wool contenders are less durable than synthetic options, but they don't hold onto odor at all. Of these, the Kari Traa Rose H/Z proves to be the most durable. Unlike the Smartwool and Capilene Air tops that have the least durable construction in this review, it offers a tightly-knit face fabric that doesn't snag. The fibers are seemingly shorter and have proven to be more durable and a better option for those needing a top for high-friction sports like canyoneering, bushwacking, or rock climbing.

Moving uphill with a tight running pack that is fully loaded is a great way to test abrasion resistance. We love that this lightweight layer is strongly constructed with great durability all around.
Moving uphill with a tight running pack that is fully loaded is a great way to test abrasion resistance. We love that this lightweight layer is strongly constructed with great durability all around.

Lighter weight contenders like the Smartwool 150 and Oasis 200 prove to offer great durability over our testing periods. While these two haven't been tested as long, online reviewers affirm the durability of these pieces. As the years go on, we will get to see how the competition plays out.

A Note on Odor
In all our tests, the synthetic shirts constructed of polyester typically smell more over time than those made of merino wool. We also found that merino wool tops could be worn for multiple excursions without washing before odor became an issue. Despite a companies efforts to develop odor-resistant fabrics with a polyester design, we found that they inevitably smell over time, whereas merino wool allows odors to wash away. Some of our testers prefer merino wool for this one simple fact.

On Rappel! Alison Lay hangs around comfortably as the wind picks up during our descent of Lotta Balls in Red Rocks  Nevada. The Arc'teryx Rho LT Zip offers great all-around protection and performance on its own and in a layered system.
On Rappel! Alison Lay hangs around comfortably as the wind picks up during our descent of Lotta Balls in Red Rocks, Nevada. The Arc'teryx Rho LT Zip offers great all-around protection and performance on its own and in a layered system.

Conclusion


The layer that lays next to your skin is integral for keeping you warm and comfortable while exploring the great outdoors. Whether you're snuggling up next to the fire or shredding on a double black at the ski hill, you must find one of high value and function for your purpose. With many options on the market, make sure you choose one without cotton in its architecture and use our review to help point you in the right direction.


Amber King