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Smartwool Classic Thermal Merino 1/4 Zip Review

An uber comfortable, warm, and breathable 100% Merino wool base layer for the coldest of conditions
smartwool classic thermal merino 1/4 zip base layer review
Credit: Smartwool
Editors' Choice Award
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Price:  $115 List | $86.25 at Backcountry
Compare prices at 2 resellers
Pros:  Supremely warm, exceptionally comfortable, front zip, shoulder panels keep things comfortable with a heavy pack
Cons:  More delicate than others, pricey, wool may lose shape and sag without proper care
Manufacturer:   Smartwool
By Justin Simoni ⋅ Review Editor  ⋅  Nov 12, 2022
Our Editors independently research, test, and rate the best products. We only make money if you purchase a product through our links, and we never accept free products from manufacturers. Learn more
80
OVERALL
SCORE


RANKED
#1 of 18
  • Warmth - 25% 9.0
  • Breathability - 20% 7.0
  • Comfort and Fit - 20% 9.0
  • Durability - 15% 7.0
  • Drying Speed - 10% 6.0
  • Layering Ability - 10% 9.0

Our Verdict

The ultra cozy, super soft, and toasty warm 250 g/m² 100% Merino wool is what makes the Smartwool Classic Thermal Merino ¼ Zip our natural pick for top accolades. Flatlock seams throughout, shoulder panels, and a padded zipper ensure that the only thing that comes in contact with your skin is wool and more wool. Wool excels at both warmth and breathability, and the Classic Thermal is no exception. Keep it underneath your other layers, as alone the wool fabric is more delicate than others. This layer's performance in warmth and breathability are what makes wool a popular choice in the first place. You won't be disappointed.

Compare to Similar Products

 
Awards Editors' Choice Award Top Pick Award Best Buy Award Best Buy Award  
Price $86.25 at Backcountry
Compare at 2 sellers
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$59.99 at Amazon
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Pros Supremely warm, exceptionally comfortable, front zip, shoulder panels keep things comfortable with a heavy packUnique seamless fabric paneling, warm and lofty Merino wool blend fabric, long sleeves and torsoSoft and stretchy fabric gives freedom of movement, great value, thumb loopsAffordable, very warm, fashionable fit, breathableExtremely breathable, lightweight, dries fast, super affordable
Cons More delicate than others, pricey, wool may lose shape and sag without proper careWeak durability keeps this top a dedicated base layer, seams found converging in pinch points, priceyNot as warm as wool layers of the same weight, risk of smelling if left unwashed after useFiner thread Merino is not quite as durable, slightly itchy, shoulder top seamsPoor fit, not very warm, not super durable, stinky
Bottom Line An uber comfortable, warm, and breathable 100% Merino wool base layer for the coldest of conditionsOne of the best midweight base layers for when you need warmth and freedom of movement thanks to its fabric blend and seamless ventilation patternOne of our favorite super stretchy, soft, and warm synthetic base layers for cool to cold conditionsThis top delivers the fine qualities of a Merino wool base layer without the extreme costThis top is an impressively breathable and lightweight base layer built for activities where you are creating a lot of heat
Rating Categories Smartwool Classic T... Smartwool Intraknit... Cotopaxi Liso Top Meriwool Merino 250... Helly Hansen Lifa S...
Warmth (25%)
9.0
8.0
6.0
9.0
5.0
Breathability (20%)
7.0
7.0
7.0
7.0
8.0
Comfort and Fit (20%)
9.0
8.0
9.0
7.0
7.0
Durability (15%)
7.0
7.0
8.0
5.0
9.0
Drying Speed (10%)
6.0
8.0
9.0
9.0
8.0
Layering Ability (10%)
9.0
8.0
8.0
6.0
6.0
Specs Smartwool Classic T... Smartwool Intraknit... Cotopaxi Liso Top Meriwool Merino 250... Helly Hansen Lifa S...
Material 100% Merino wool 53% Merino wool, 45% polyester, 2% elastane 84% recycled polyester, 16% spandex 100% Merino wool 100% Lifa Dry
Fabric Weight 250 g/m² 208 g/m² 200 g/m² 250g/m² 125 g/m²
Weight (size large) 11.3 oz 8 oz 8.5 oz 10.1 oz 5.2 oz
Available Cuts Crew, 1/4 zip, hoodie Crew, 1/4 zip Crew Crew Crew
Thumb Loops? No No Yes No No
Air Dry Test 70 min 45 min 40 min 40 min 45 min
Fit Semi-fitted Slim fit Semi-fitted Slim fit Slim fit
Stitching Flatlock seams Flatlock seams (mesh inserts are seamless 3D) Flatlock seams Flatlock and flat seams Flatlock seams
Dryer Safe? Yes No Yes No Yes
Shoulder Top Seams? No Yes No Yes Yes
Drop Tail Hem? No Yes No No No

Our Analysis and Test Results

The quality, 100% Merino wool used in the Classic Thermal 1/4 Zip comes with some amazing qualities that we love seeing in a base layer. The warmth of wool is well known, and the 250 g/m² weight of this top makes it one the warmest we've tested. Wool also comes with unique breathability characteristics, naturally wicking away perspiration from the surface of your skin, helping to keep you comfortable rather than soggy. The Merino wool used in the Classic is soft and lofty, and we didn't notice any of the scratchiness you may experience with a lower-quality piece. The semi-fitted cut leaves a lot of wiggle room for various body types and also allows you to pair this top with another leaner and stretchy base layer when you're looking for even more flexibility in your layering system. Can we say anything negative about this layer? Wool is just a more delicate material than synthetics, so treat it well both when wearing and caring for it to protect your investment and keep it around for many years of adventures.

Performance Comparison


smartwool classic thermal merino 1/4 zip base layer review - when temperatures starting dipping down, the smartwool classic...
When temperatures starting dipping down, the Smartwool Classic Thermal Merino 1/4 Zip keeps the goofy smile on our face.
Credit: Justin Simoni


Warmth


Toasty! The Classic Thermal 1/4 Zip scores high in our tests for warmth, thanks to its medium weight, 250 g/m² 100% Merino wool fabric. This is the heaviest weight that Smartwool uses for base layers and the heaviest weight for all base layers we test ourselves. Anything heavier and the top works less as a base layer where you want freedom of movement to be tantamount. The Classic Thermal Merino excels in cold, wintry conditions.


Several features of this base layer enhance its warmth. The high collar rests just above the chin when the shirt is fully zipped up, keeping drafts from sneaking up from the top. The sleeves are extra long to completely cover up your arms, no matter your ape index. And the front ¼ zipper itself facilitates thermoregulating when you need to bundle up for extra warmth or unzip to dump excess heat.

smartwool classic thermal merino 1/4 zip base layer review - this base layer is one of the heaviest we've reviewed and is also...
This base layer is one of the heaviest we've reviewed and is also one of the warmest.
Credit: Justin Simoni

Breathability


For such a thick and warm base layer, the Classic Thermal fared well in our breathability tests. Being warm is one thing, but you don't want to be soaking in your own sweat underneath your mid and outer layers. The renowned natural moisture-wicking qualities of Merino wool are one of the reasons why most of the thermal base layers we test and review utilize it. Wool, being naturally hydrophobic, transports sweat from the skin surface towards the surface of the base layer, keeping you drier. This magical dance of wool to keep you dry and warm is seen most in thicker wool base layers.


In the real world, we tested this layer on all-day bike rides, cold camping nestled in our sleeping bags, vigorous hikes to summit the mountains in the backcountry, and haunting the local coffee shop. We're more than pleased, but our time in this base layer cemented our belief that this is a great top for cold-weather conditions in particular; you'll just get too hot if the sun starts shining brightly enough to melt the snow around you.

smartwool classic thermal merino 1/4 zip base layer review - the front 1/4 zip on the smartwool classic thermal merino helps with...
The front 1/4 zip on the Smartwool Classic Thermal Merino helps with dumping excess heat quickly, coming in handy when you're layered up and conditions change quickly.
Credit: Justin Simoni

Comfort and Fit


We found the Classic Thermal has a looser fit than many of the athletic, skin-hugging Merino wool and wool blend tops we've tested. This may be the way to go for a heavier layer, as tighter tops also need to be a bit stretchy to articulate with the body. The Classic Thermal is 100% Merino wool, so it lacks that super stretch and recoil we've seen in thin Merino blends and synthetics. Although it is designed to be a next-to-skin piece, this looseness also allows it to be worn as a mid-layer, with a lighter-weight base layer underneath. For less extreme conditions, we found ourselves utilizing this configuration often when the afternoon sun made it too warm to want to wear the Classic.


The hand of this fabric is absolutely creamy in its softness, with no feeling of scratchiness at all. This is important, as the collar comes up high on the neck — an oftentimes sensitive area — reaching up to the chin, helping keep drafts from entering from the top.

Careful consideration was made to the placement of the flatlock seams and fabric patterns used in the construction of the Classic Thermal Merino. In particular are the addition of shoulder panels to move the seams off the crest of your shoulders and allow better comfort when shouldering a heavy pack. Our main tester's larger-than-usual shoulders fared well with this top's generous allowance of space as well. The front zip is also padded with an additional wool panel so the potentially freezing-cold zipper never touches your skin. The zipper itself is a great addition to any base layer to help thermoregulate by allowing you to dump excess heat when needed and bundle up afterward. If you don't mind the slight weight penalty a zipper adds, it's a feature to look out for in any base layer you decide to grab.

smartwool classic thermal merino 1/4 zip base layer review - a slightly loose fit and long sleeves means it's easy to bundle up...
A slightly loose fit and long sleeves means it's easy to bundle up when the wind starts whipping up
Credit: Justin Simoni

Durability


As usual, "100% Merino wool" equates to less than bulletproof durability, and the Classic Thermal is no exception. The thicker 250 g/m² of this wool base layer still garnered similar results in our harsh abrasion test as a 150 g/m² Merino wool base layer: holes were ripped right through the fabric. This is just the nature of 100% Merino wool and something to understand when buying anything made of the material. We suggest using this top in its role as a base layer first and foremost, where it's protected underneath more durable mid and outer layers. To extend the life of this base layer, we'd suggest washing it only when necessary. The manufacturer does state that this top can be thrown in the dryer on low, but we prefer to hang it to dry whenever possible.


In the real world, we found the quality of the wool, seams, and zipper to be excellent, with no premature rips, tears, or breakage noticed. The delicateness of the wool is a fair compromise given the performance of wool as a base layer material. If not abused, this worthy investment should last the user a very long and vibrant life underneath flashier accouterments.

smartwool classic thermal merino 1/4 zip base layer review - even though the 100% merino wool 250 g/sm is heavy weight for a base...
Even though the 100% Merino wool 250 g/sm is heavy weight for a base layer, our harsh abrasion test ripped right through the fabric.
Credit: Justin Simoni

Drying Speed


Drying speed can usually be hypothesized to a fairly accurate degree by looking at the type and the thickness of the material. For example: a thicker, 250 g/m² 100% Merino wool base layer like the Classic Thermal should hypothetically dry at a slower rate than both thinner woolies and most all synthetics. This is what our lab tests then confirmed.


Wool is used in base layers as it's an excellent insulator with good warmth and breathability characteristics. As a hygroscopic material, wool actually actively adsorbs water. In other words, it traps water between its fibers rather than absorbing and permeating it throughout the fabric and wetting it out. This can cause slower dry times. Roughly 30% of the wool's weight in water can be trapped before feeling all that wet on your skin.

There have been claims that wool can be warmer than a synthetic when wet and that wool even generates heat when it dries. But these claims are a little exaggerated for us. We will say that the natural wicking qualities of wool help you to at least feel dryer while water and perspiration move from your skin to the exterior of the fabric.

Out of the weeds and back to our real-world tests, we took the Classic Thermal up to the summit of Longs Peak in Colorado during wintry conditions, mostly worn as a mid-layer, where it performed exceptionally to keep us both warm and dry. We also slept in it in our sleeping bags on a five-day backpacking trip and woke up just as dry and comfortable.

smartwool classic thermal merino 1/4 zip base layer review - the smartwool classic thermal merino 1/4 zip is great as a base...
The Smartwool Classic Thermal Merino 1/4 Zip is great as a base layer to wear while camping as the 100% Merino wool is highly breathable, keeping you both warm and dry while nestled in your sleeping bag.
Credit: Justin Simoni

Layering Ability


For how soft and thick the 250 g/m² Merino wool fabric is, the Classic Thermal slides smoothly over our skin and most of our mid layers well. The low-profile flatlock seams don't contribute any problems, and only the most scratchy of mid layers would cause issues by hooking into the soft, flocculent wool. Something like our heavy-down sweater with a nylon exterior couldn't have presented less friction against each other.


Since this is one of the heaviest base layers we've tested and it has a looser, semi-fitted profile, we found ourselves using it as a mid-layer on some trips, with a much thinner and tighter base layer underneath. This allowed us to take off the very warm Classic Thermal Merino, and have something else underneath. The high collar makes the front zip easily accessible underneath additional layers, so fishing around to dump some heat was painless. As we mention in other parts of this review, because of the delicate nature of 100% Merino wool fabric, you wouldn't want to use this base layer as a dedicated layer-of-one, like you can with some of the other more durable synthetics out there. Traveling through tough terrain, like off-trail travel through thick brush or exploring slot canyons, will likely cause premature damage to this top.

smartwool classic thermal merino 1/4 zip base layer review - the smartwool classic thermal merino ¼ zip works well as both a...
The Smartwool Classic Thermal Merino ¼ Zip works well as both a heavy base layer and a lighter mid layer, thanks to its soft Merino wool that won't catch on anything but the most scratchy of garments.
Credit: Justin Simoni

Should You Buy the Smartwool Classic Thermal Merino?


If you're looking for a warm, soft, comfortable, breathable 100% wool base layer, we think that the Classic Thermal is an absolutely rock-solid choice. It looks good, feels great, and performs even better. Take note of how delicate 100% Merino wool can be, as well as caring for wool when you need to wash and dry it. Cared for correctly, the Classic Thermal Merino should be a righteous partner for your cold-weather adventures for years to come.

smartwool classic thermal merino 1/4 zip base layer review - one of the big strengths of the smartwool classic thermal merino...
One of the big strengths of the Smartwool Classic Thermal Merino ¼ Zip is its versatility when it comes to layering up. As a base layer, it excels at the coldest conditions. As a mid layer, it adds more warmth to a thinner base layer worn underneath.
Credit: Justin Simoni

What Other Base Layers Should You Consider?


If the cost of the Classic Thermal is beyond your reach, the Meriwool Merino 250 Long Sleeve is a solid option to dip your toes into the world of 250 g/m² 100% Merino wool tops. It does lack a front zip, and the wool isn't as soft or lofty. If you would rather go synthetic, consider the Under Armour ColdGear Base 4.0 Crew, the heaviest and warmest synthetic base layer we've tested. The ColdGear tested much better in two areas: durability and drying speed. But for the weight of the fabric, it's just not as warm or breathable. If you are looking for a high-performance wool top that's not quite as thick, warm, or heavy, move laterally toward the Smartwool Intraknit Thermal Merino. The Intraknit has a more athletic fit, an even loftier wool blend, and slightly better warmth for its weight.

Justin Simoni
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