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Smartwool Intraknit Thermal Merino Review

One of the best midweight base layers for when you need warmth and freedom of movement thanks to its fabric blend and seamless ventilation pattern
smartwool intraknit thermal merino base layer review
Credit: Smartwool
Top Pick Award
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Price:  $125 List | $72.00 at Backcountry
Compare prices at 2 resellers
Pros:  Unique seamless fabric paneling, warm and lofty Merino wool blend fabric, long sleeves and torso
Cons:  Weak durability keeps this top a dedicated base layer, seams found converging in pinch points, pricey
Manufacturer:   Smartwool
By Justin Simoni ⋅ Review Editor  ⋅  Nov 12, 2022
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77
OVERALL
SCORE


RANKED
#3 of 18
  • Warmth - 25% 8.0
  • Breathability - 20% 7.0
  • Comfort and Fit - 20% 8.0
  • Durability - 15% 7.0
  • Drying Speed - 10% 8.0
  • Layering Ability - 10% 8.0

Our Verdict

The Smartwool Intraknit Thermal Merino excels at keeping you warm while also being super breathable: not an easy trick to pull off. This is accomplished partly by using a soft, lofty Merino wool blend that's got a looser weave than other base layers, allowing your sweat to wick from your skin out through the fabric. The thin, athletic fit keeps the Intraknit close to your body, and the slight stretch of the spandex added to the blend helps keep movement unimpeded. This top also uses the namesake Intraknit tech — a SmartWool exclusive, where seamless panels of material in the middle back, armpits, and top of the shoulder are not as thick, allowing for more ventilation. All this engineering does come at the price of durability: you'll want to use this as a dedicated base layer.

Editor's Note: This review was updated on November 12, 2022, after going through a full retest against our new Fall lineup.

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Awards Top Pick Award Editors' Choice Award Top Pick Award Best Buy Award Best Buy Award 
Price $72.00 at Backcountry
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$115.00 at Backcountry
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$145 List$65 List$60 List
$59.99 at Amazon
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Pros Unique seamless fabric paneling, warm and lofty Merino wool blend fabric, long sleeves and torsoSupremely warm, exceptionally comfortable, front zip, shoulder panels keep things comfortable with a heavy packBreathable and stretchy, useful features such as hood and thumb loops, highly adaptable to wide range of conditionsSoft and stretchy fabric gives freedom of movement, great value, thumb loopsAffordable, very warm, fashionable fit, breathable
Cons Weak durability keeps this top a dedicated base layer, seams found converging in pinch points, priceyMore delicate than others, pricey, wool may lose shape and sag without proper careSlim athletic fit requires a slim athletic body type, expensive, not as durable as cheaper syntheticsNot 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 seams
Bottom Line One of the best midweight base layers for when you need warmth and freedom of movement thanks to its fabric blend and seamless ventilation patternAn uber comfortable, warm, and breathable 100% Merino wool base layer for the coldest of conditionsUnique features like thumb loops and a hood makes this Merino wool blend base layer super versatileOne 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 cost
Rating Categories Smartwool Intraknit... Smartwool Classic T... Black Diamond Solut... Cotopaxi Liso Top Meriwool Merino 250...
Warmth (25%)
8.0
9.0
7.0
6.0
9.0
Breathability (20%)
7.0
7.0
7.0
7.0
7.0
Comfort and Fit (20%)
8.0
9.0
9.0
9.0
7.0
Durability (15%)
7.0
7.0
6.0
8.0
5.0
Drying Speed (10%)
8.0
6.0
8.0
9.0
9.0
Layering Ability (10%)
8.0
9.0
10.0
8.0
6.0
Specs Smartwool Intraknit... Smartwool Classic T... Black Diamond Solut... Cotopaxi Liso Top Meriwool Merino 250...
Material 53% Merino wool, 45% polyester, 2% elastane 100% Merino wool 78% Merino wool, 22% polyester 84% recycled polyester, 16% spandex 100% Merino wool
Fabric Weight 208 g/m² 250 g/m² 150 g/m² 200 g/m² 250g/m²
Weight (size large) 8 oz 11.3 oz 8 oz 8.5 oz 10.1 oz
Available Cuts Crew, 1/4 zip Crew, 1/4 zip, hoodie Crew, 1/2 zip hoody Crew Crew
Thumb Loops? No No Yes Yes No
Air Dry Test 45 min 70 min 45 min 40 min 40 min
Fit Slim fit Semi-fitted Slim fit Semi-fitted Slim fit
Stitching Flatlock seams (mesh inserts are seamless 3D) Flatlock seams Flatlock seams Flatlock seams Flatlock and flat seams
Dryer Safe? No Yes No Yes No
Shoulder Top Seams? Yes No No No Yes
Drop Tail Hem? Yes No No No No

Our Analysis and Test Results

Of all the base layers we've tested, the Intraknit Thermal Merino comes with the most buzzwords. What sets this base layer apart from all others we've tested is the Intraknit fabric: this top is made with seamless panels of fabric that have slightly different characteristics. Fabric that's slightly thinner for better ventilation is located in areas one perspires the most. More flexible fabric is found on the elbows, explicitly designed to bend and flex without stretching out. The rest of the shirt is covered in warmer fabric. Sounds complicated, but the end product looks much like any other thermal base layer, and these panels are almost visually imperceptible unless you know what to look for. But wearing the Intraknit reveals all this engineering does what it says it will. The result is a warm, lively, and svelte for its warmth top, perfect for those who love to move fast in the cold.

Performance Comparison


smartwool intraknit thermal merino base layer review - the midweight intraknit layers well with other performance-type...
The midweight Intraknit layers well with other performance-type outer layers, and is heavy enough to be used as a mid layer itself
Credit: Drew Crittenden


Warmth


The Intraknit Thermal scored well in our warmth tests, especially for the overall weight of the top. This top will act similarly to a 200 g/sm Merino wool layer while weighing on the scale like a 175 g/sm base layer. The soft, Intraknit fabric is excellent at trapping pockets of air between its weaved pattern and visually looks less compressed than many other base layers we've tested.


This warmth isn't applied uniformly throughout the base layer. For the men's model, the center back, armpits, and top of the shoulders are ventilated more than the rest of the top. This is achieved using less dense fabric panels than what's used in the rest of the base layer. These panels are subtle, as the technology used means there aren't any seams between them. If you are sweaty like our main tester, the Intraknit fabric may be your ticket for a more enjoyable time being active in the cold.

smartwool intraknit thermal merino base layer review - the merino wool/synthetic blend leads to an engineered fabric that's...
The Merino wool/synthetic blend leads to an engineered fabric that's warmer than many 100% Merino wool layers of the same weight.
Credit: Justin Simoni

Breathability


The woven tech of the Intraknit Thermal also allows it to be quite breathable. Both wool and polyester layer are hydrophobic, meaning they'll excel at their job of wicking moisture from the surface of your skin and depositing it onto the exterior of the fabric instead of letting it sit and soak in. The Intrakit weave is also looser than many of the wool and wool blends we've tested, allowing water to move through more easily.


In our real-world tests out in Rocky Mountain National Park on a cool Fall day, we found the Intraknit Thermal Merino worked well as a base layer as we were trudging up to above treeline. Mountain climbs from low altitude to out past treeline are sometimes tricky, as it's easy to overheat quickly in the trees where you're shielded from wind to weather, only to freeze above treeline care of a sweated-out baselayer. Thanks to staying reasonably dry, that didn't happen to us, and we could simply put on an outer layer in confidence.

smartwool intraknit thermal merino base layer review - the smartwool intraknit thermal merino is perfect for keeping alpine...
The Smartwool Intraknit Thermal Merino is perfect for keeping alpine start chills at bay.
Credit: Drew Crittenden

Comfort and Fit


We'd describe the fit of the Intraknit as "body hugging." It's a slim fit with fabric that has quite a bit of stretch and recoil strength. As we noted above for warmth, this layer has seamless panels where different fabric characteristics are expressed; some panels have better breathability and less warmth. Other panels, like on the elbows, allow better movement — and this will hopefully help with wear. No matter the panel, the 53% Merino wool, 45% polyester, and 2% elastane blend feels a little more flocculent and scratchier than other 150-200 g/sm wool/wool blend base layers we've tested.


Still, overall comfort is better than most, and we're happy that all actual seams on the Intraknit Thermal Merino are of the flatlock variety. There is also a drop tail hem, the sleeves are generously long, and the neckline is not overly tight. That said, some less-than-ideal patterning leaves some interesting seam junctions, including by the armpits. If you have larger shoulders, this may turn into a pressure point with this slim fitted base layer. A seam also runs on top of the shoulders, which can cause chafing for those who wear a heavy pack. We would have loved to see a design that removes the top shoulder seam by utilizing raglan sleeves or an additional top shoulder panel like we have noticed in some other base layers.

smartwool intraknit thermal merino base layer review - the intraknit's seamless panels can be seen here in the chevrons of...
The Intraknit's seamless panels can be seen here in the chevrons of the back where the fabric allows more ventilation, and the hexagon located on the elbow of the sleeve, which allows more articulation.
Credit: Justin Simoni

Durability


As is typical for most wool and wool blends that we've tested, durability is not this layer's strong suit. Even though almost half of the Intraknit is made up of tougher synthetic material, the weakest link is still the delicate wool. In our harsh abrasion test, we were able to rip open fairly large holes in the fabric — again: not uncommon for wool/wool blends of any thickness. Underneath a mid and outer layer would be the best place for this layer to live out a long, fruitful life.


In our tests, we found the quality and stitching to be top-notch, as we expect from this reputable brand. Multiple washings created a bit of fuzz on the surface, but nothing out of the ordinary for a Merino wool blend shirt. This would be a base layer you would want to absolutely avoid putting into the clothes dryer at any heated temperature, given both wool and elastane are part of the fabric blend. Wool has a tendency to both shrink and lose its form; elastane will lose its elasticity when exposed to heat.

smartwool intraknit thermal merino base layer review - our harsh abrasion test cut right through the exterior layer of the...
Our harsh abrasion test cut right through the exterior layer of the Intraknit fabric, exposing the inner layer.
Credit: Justin Simoni

Drying Speed


Our on-the-line drying speed test showed some of the best marks for this layer for wool and wool blends. The loose weave of the Intraknit easily gave up its moisture instead of locking it up underneath a tighter weave. Being one the loosest weaves of anything we've tested means that this base layer dries as fast as a lighter weighted fabric.


Drying speed is closely coupled to breathability; if the former is fast, often the latter has good performance as well, and this does seem to be the case for the Intraknit Thermal. As we've noted, this may be a great choice of base layer for those who sweat generously or find themselves traveling in more humid climates.

smartwool intraknit thermal merino base layer review - on the line drying time was excellent for a midweight base layer...
On the line drying time was excellent for a midweight base layer, and usually translates to good breathability while wearing it.
Credit: Justin Simoni

Layering Ability


The body-hugging design of the Intraknit Thermal Merino makes it comfortable on its own, and it also makes it perfect for laying on mid and outer layers. The slight stretch of the fabric helps keep pinch points and chafing at a minimum which is important in the cold when you're not in a great position to start peeling off layers just to adjust your base. The Intraknit seamless paneling also helps with layering. Since some panels have more breathability in key spots, others are more stretchy; this should altogether help with keeping the base layer comfortable to wear underneath your other layers. We personally found this baselayer nothing we had to think about at all — no news is good news, and we could instead focus on our outdoor adventures.


Additional features like long sleeves and a drop tail hem make riding up less of a problem. The fabric's exterior is softer and fuzzier than many of the base layers we've tested, and this can sometimes hook into mid-layers like gridded fleece, much like velcro. If you're using a mid-layer like that, this could be a base layer to avoid.

smartwool intraknit thermal merino base layer review - the smartwool intraknit thermal merino makes a great midweight...
The Smartwool Intraknit Thermal Merino makes a great midweight baselayer for light and fast adventures in cold environments.
Credit: Drew Crittenden

Should You Buy the Smartwool Intraknit Thermal Merino?


We think this top makes a great cold-weather base layer. If that's what you're looking for, pull the trigger. Just make sure the slimmer fit works with your body type, and plan to wear this base layer underneath more durable layers. Price could be a deciding factor: the Intraknit tech does not come at a discounted price. Do we think it's worth the MSRP? In the end, we do, especially for those looking for a little more performance out of their base layer, while still saving some grams.

smartwool intraknit thermal merino base layer review - the slim, athletic fit of the smartwool intraknit thermal merino...
The slim, athletic fit of the Smartwool Intraknit Thermal Merino hugs the body, which helps facilitate the wicking nature of the stretchy merino wool blend fabric.
Credit: Justin Simoni

What Other Base Layers Should You Consider?


For an even warmer layer, the Smartwool Classic Thermal Merino 1/4 Zip is our top choice. It does lack the Intraknit weaving but has a nice front quarter zipper to aid with breathability. For something just a little lighter, look at the Ortovox 185 Rock'N'Wool Long-Sleeve, which features similar soft Merino wool that lofts up somewhat similar to the Intraknit. For a more budget-friendly option, look no further than the Meriwool Merino 250 Long Sleeve, which will give you similar warmth with the compromise of being a little less durable, and a little heavier.

Justin Simoni
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