Hands-on Gear Review

SmartWool Merino 250 Base Layer Review

SmartWool Merino 250 Base Layer
Editors' Choice Award
Price:  $100 List | $76.73 at REI
Compare prices at 4 resellers
Pros:  Extremely comfortable, warm for the weight, stylish, odor resistant, breathable
Cons:  Expensive, limited durability, dries relatively slowly
Bottom line:  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.
Editors' Rating:   
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Material:  100% merino wool
Fabric Weight:  Midweight - 250 g/m 2
Thumb Loops?:  No
Manufacturer:   Smartwool

Our Verdict

The SmartWool Merino 250 Base Layer returns this year as a back-to-back champion in our latest review of base layers. In over a year of searching, we still haven't found a product that quite stacks up to this one. The super soft merino wool featured in this model is so good, you might not believe it's actually wool until you check the specs. We are impressed with its warmth, breathability, and layering ability, but most significantly, its comfort and fit, which is why it wins our Editors' Choice award.

There is a special feeling we get when donning this all-star garment. The fabric is light and cozy with a gentle stretch that forms to any movement. Its comfort is combined with handsome styling and technical advantages that make it equally useful for a date with Eve or Everest. Our psych was only slightly tempered by small concerns about drying speed and durability, but when viewed across all our tests and analyses, this model is the top dog. Or top sheep?

Name Change
SmartWool switched up the name on this top to "Merino 250 Base Layer," previously known as the SmartWool NTS 250. Other than adding some new color options, that's the only change. It's still available at online retailers in its old name, but know that it's the same shirt under both names.



RELATED REVIEW: The Best Long Underwear and Base Layer for Men

Our Analysis and Test Results

Review by:
Ross Robinson

Last Updated:
Monday
December 19, 2016

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The balance of warmth, breathability, and comfort found in the Merino 250 Base Layer by Smartwool made it our favorite base layer. While expensive ($100) and somewhat delicate, the quality construction and thoughtful design are characteristics that will be appreciated by any outdoor adventurer. Just slip into this bad boy once, are we're convinced you'll be singing a happy tune straight away.

Performance Comparison


The Editors' Choice award winner celebrated above-average to exceptional scores across the board. We were psyched to wear it on nearly any trip in the outdoors.
The Editors' Choice award winner celebrated above-average to exceptional scores across the board. We were psyched to wear it on nearly any trip in the outdoors.

Warmth


At 250 g/m², this top is Smartwool's thickest base layer offered. It is also their most popular. Our testers felt this weight provided an ideal amount of warmth in most temperatures offered during spring, fall, and winter. This product displayed a great warmth to weight ratio, too, only weighing 9.6 ounces. During the heat of summer, consider choosing a lighter option like running-specific shirts.

While this product is quite warm for its weight  it also regulates a wide range of temperatures very well  as shown here hiking in 70°F temps in a sunny desert canyon in South America.
While this product is quite warm for its weight, it also regulates a wide range of temperatures very well, as shown here hiking in 70°F temps in a sunny desert canyon in South America.

We loved how this top stayed nice and warm when temperatures dropped, but also remained comfortable as the mercury rose. It served us well as both a first layer and a mid-layer when skiing the early winter slopes of Lake Tahoe. We even wore this top comfortably in temperatures up to 70°F with a loaded pack on a sunny desert day in Colca Canyon, Peru, when other base layers of its warmth rating would supply us with a sweaty sauna. This kind of versatility in warmth, without overheating, was unrivaled amongst the competitors we selected for this review.

Breathability


Like the rest of the merino wool long underwear in this review, this top is quite breathable. We give credit for this performance to the advantageous properties of natural fibers, and the snug next-to-skin fit designed by SmartWool. Water vapor from the skin passed through the fibers without condensing, as advertised. Even when we worked up a sweat in the backcountry, this layer quickly moved the moisture in the microclimate between skin and shirt to the external environment.

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.

Comfort and Fit


The most outstanding qualities of the Merino 250 lie in its comfort and fit. More than any other long underwear reviewed, this top begged to be worn. Its merino wool was one of the softest fabrics overall, and the sensible design left our testers with no complaints. The length of the waist is just a bit longer than almost all other tops with a slight curve in back to hide a plumber's crack.

The fit  design  and fabric flexibility lend themselves to great mobility  which we appreciated when scrambling through granite in the California Sierras.
The fit, design, and fabric flexibility lend themselves to great mobility, which we appreciated when scrambling through granite in the California Sierras.

If you've got moves, this base layer is prepared to move with you. The more elastic weave of the Smartwool material helped it conform to the body better, following movements, and rising up less. The flat and smooth stitching is thoughtfully placed in areas that avoid rubbing and chafing, even under a backpack. Even without underarm or side gussets, the stretch and flex of this top are enough to provide unhindered mobility. Instead of coming close with fit and comfort, SmartWool perfected this category. If the merino wool of even this model is too much for you, though, check out some the very comfortable synthetic models.

Drying Speed


In our drying speed test, the SmartWool took a while to dry after being completely saturated. Being one of the thicker fabrics in this review, we weren't very surprised by this result. It did dry faster than some thinner products, though.

This SmartWool product doesn't dry as fast as many of the thinner products in this review  but the fact that it still insulates while wet makes this issue less severe.
This SmartWool product doesn't dry as fast as many of the thinner products in this review, but the fact that it still insulates while wet makes this issue less severe.

During this test, we were impressed with this top's resistance to absorbing moisture. Testers had to agitate the material, and all the merino wool layers, underwater before they would become completely saturated. There seems to be some truth to advertisers' claims that merino wool can absorb up to 30% moisture by weight before feeling wet.

Durability


The thickness of this merino wool should help it last longer than the other wool products. After three months, there was only one loose string hanging from the hemmed bottom, which appeared unaffected concerning performance. The seams are stitched with expert quality, and we were impressed by the use of heavier stitching in high-stress areas, and more moderate stitching in places of lower strain.

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

Unfortunately, comparable synthetic tops are just more resistant to punctures and abrasion overall. SmartWool made a nice garment with quality in design and stitching, but there are limitations to the fabric. Yet, a subtle upside for merino wool in durability is its natural antibacterial qualities and a resistance to absorbing moisture. These attributes mean that it will not develop unpleasant odors like synthetics; leading to fewer cycles through the washing machine, an extended life, and happier hiking companions.

Merino wool is delicate  and simply won't last forever  but the thicker fabric of this model should last longer than its thinner wool competition.
Merino wool is delicate, and simply won't last forever, but the thicker fabric of this model should last longer than its thinner wool competition.

Although SmartWool claims this product is dryer-safe, we think flat drying merino wool products is a good idea. As these products aren't the most rugged, we prefer avoiding the rumble and tumble of the dryer machine.

Layering Ability


This contender proved to be very versatile in its layering abilities. Whether worn over a t-shirt, another base layer, or under a jacket or mid-layer, this product delivered comfort and mobility without a hiccup.

When skiing in the Sierras  we liked the comfy  warm  and flexible combination of the SmartWool as a base layer and Arc'teryx model serving as a mid-layer  with a hardshell overtop.
When skiing in the Sierras, we liked the comfy, warm, and flexible combination of the SmartWool as a base layer and Arc'teryx model serving as a mid-layer, with a hardshell overtop.

We really like the elasticity of this shirt that helps the top to stay in place and form to movements even when insulating layers on top were acting to displace it. This elasticity also allows it to be worn as an insulating layer itself, stretching to fit over a separate shirt. These dual uses mean that it can be worn comfortably across a wide range of temperatures or activity levels.

Reviewer Ross Robinson wearing the Mountain Hardwear model over the Smartwool Merino 250 for solid insulation  breathability  and comfort.
Reviewer Ross Robinson wearing the Mountain Hardwear model over the Smartwool Merino 250 for solid insulation, breathability, and comfort.

If you're looking for a model that performs great as a base or mid-layer, this model is where your search ends.

Best Applications


Apart from the high temps of summer, this top has few situations where it could not be used. Its most ideal use is serving as a true base layer in cold weather activities; where its delicate construction is protected from scrapes by extra layers on top. It is equally functional (and fashionable) at a dinner party as at an unplanned bivy. Consider taking it along on an overseas vacation where laundry might be hard to come by because its resistance to odors keeps it socially acceptable between belated washes. A UPF rating of 50+ makes it an option for rare situations with extreme sunlight, like days on the water or snow, or at high altitudes.

We liked this top for bombing down snowy slopes  as well as crashing parties.
We liked this top for bombing down snowy slopes, as well as crashing parties.

Value


We won't pretend this product is cheap, costing $100. However, we do think the versatile performance it provides justifies the cost. Keep in mind that for outdoor uses you only need one base layer. If you treat it kindly and don't overwash, this shirt should last for quite a long time.

Merino wool is our favorite fabric  and the SmartWool model was the best shirt of our favorite material.
Merino wool is our favorite fabric, and the SmartWool model was the best shirt of our favorite material.

Conclusion


There are several stand-out features that helped this long underwear top take home our Editors' Choice award—warmth, breathability, and comfort come to mind—but overall it was the total combination of these qualities into one shirt that brought it out on top. Although the reviewing process is over, we'll continue grabbing this shirt out of our closet anytime the temperature cools, chills, or even becomes frigid. We found several outstanding products in this year's long underwear review, but if we could only recommend one base layer, this would be it.

Ross Robinson


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OutdoorGearLab Member Reviews


Most recent review: April 9, 2018
Summary of All Ratings

OutdoorGearLab Editors' Rating:  
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 (5.0)
Average Customer Rating:  
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 (5.0)

100% of 1 reviewers recommend it
 
Rating Distribution
2 Total Ratings
5 star: 100%  (2)
4 star: 0%  (0)
3 star: 0%  (0)
2 star: 0%  (0)
1 star: 0%  (0)
Skier

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   Apr 9, 2018 - 12:53am
David M · Skier · Stratham, NH

I’ve owned a Smartwool 250 NTS for over 4 years and this product is unquestionably the best base layer I’ve ever owned, hands down. It’s trully a one quiver item.

I’ve worn mine Alpine skiing in sub zero degree weather, while winter climbing Mt. Washington in -45 windchill, and on overnight back country trips in late October in Yellowstone and this product has always performed at a very high level.

It’s warm, dries reasonably well, and works as both a base and mid-layer. Surprisingly Outdoor Gear Lab rated it low in durability. My experience has been quite the opposite. I’ve got probably 200+ days in this shirt and there is no obvious signs of wear and it still has kept its shape.



Bottom Line: Yes, I would recommend this product to a friend.


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