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.
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.
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. If warmth is the opposite of what you're looking for in a base layer, the Patagonia Capilene Midweight
might intrigue you.
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 sweat sauna. This kind of versatility in warmth, without overheating, was unrivaled amongst the competitors we selected for this review. The warmest model proved to be the Arc'teryx Rho AR
, but it wasn't nearly as versatile in warmer conditions.
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.
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.
The Helly Hansen Lifa Stripe Crew was the most breathable
model we found. Yet, for a more breathable and also all-around top performer, check out our Top Pick for Lightweight model, the Rab Merino+ 160
or the REI Merino Midweight
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 tasc Base Layer
featured the longest torso in this review and is the only product longer than this contender.
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 of The North Face Warm
and Arc'teryx Rho AR
The fit, design, and fabric flexibility lend themselves to great mobility, which we appreciated when scrambling through granite in the California Sierras.
In our drying speed test, the SmartWool took 41.7% more time than the Lifa Stripe Crew
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 the much thinner tasc Base Layer
and Minus33 Isolation Midweight Wool
and was outranked by the REI Merino Midweight
and the highest scoring contender, the Patagonia Capilene Midweight
During this test, we were impressed with this top's resistance to absorb 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.
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.
The thickness of this merino wool should help it last longer than the other wool products. It was clearly stronger than the blended fabric products from Rab
. After three months, there was only one loose string hanging from the hemmed bottom, which appeared unaffected in terms of 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. The most durable model we reviewed is the Mountain Hardwear Microchill 2.0
, a good choice for abuse in cold weather activities.
Unfortunately, comparable synthetic tops are just more resistant to punctures and abrasion overall. Smartwool has 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 absorb moisture. These attributes mean that it will not develop unpleasant odors like synthetics; leading to less cycles through the washing machine, an extended life, and happier hiking companions.
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.
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.
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.
This contender proved to be very versatile in its layering abilities. It was only outmatched by the ultimate layering top, the Arc'teryx Rho AR
. 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.
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. For a more one-dimensional wool product base layer, though, head over to the Icebreaker Oasis
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.
If you're looking for a model that performs great as a base or mid-layer, this model is where your search ends.
Reviewer Ross Robinson wearing the Mountain Hardwear model over the NTS Mid 250 for solid insulation, breathability, and comfort.
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 won't pretend this product is cheap; at $100, it's the third highest-priced base layer in this review. 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.
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.