This all-around favorite continues to keep us warm, dry, and comfortable in nearly any situation
Price: $110 List | Check Price at REIPros: Temperature regulation, ultra-cozy, balance of warmth and breathability Cons: Expensive, recommend special laundering, slow to air-dry Manufacturer: Smartwool
Once again, the SmartWool Merino 250 Crew earns its spot at the top of the pile of contenders. Across the board, this well-designed crew continues to impress in terms of thermoregulation, with an uncanny ability to balance warmth and breathability. Combine that with a plush, 100% merino wool weave, and we guarantee you will have to find a really good reason to want to take this layer off (like washing.) Forget about Merino's notoriously poor durability; the thick cut of this top can stand-up to multi-pitch climbs as easily as it does multi-day hut trips. It looks good, too, thanks to a handsome cut and slim fit. With a design that helps refine the phrase "simple yet elegant," we think this base layer is the best we have ever tested.
Updated Since Testing
Smartwool has rebranded the Merino 250 Crew to the Classic Thermal. The shirts use the same material, but the Classic Thermal version has a new fit and some different seamlines. Note that online stores may still be selling either version.
Our Analysis and Test Results
The 3-time Editors' Choice Award winner has received a recent upgrade from SmartWool, making the Merino 250 even more functional. A re-design of the shoulder panels moves the flatlock seams further apart, making this more comfortable when wearing a backpack and offering a more accommodating fit for those with broad shoulders.
At the time of writing, SmartWool doesn't extend their line beyond midweight options. The Merino 250 is their thickest offering, weighing in at 250 g/m² — this also solidly places it as one of the thickest in our review as well. So it should come as no surprise that this is one of the warmest layers we tested. From biting winter cold to warmer walks in the early fall sun, the versatility of this tried-and-true layer continues to impress us. Even though it is designed to be worn next-to-skin as a base layer, we often found ourselves reaching for this top to wear as a mid-layer when we needed to add a little extra warmth without adding much bulk.
When it comes to balancing warmth through a range of temperatures, the Merino 250 is our go-to choice. This makes it a near-perfect companion for fall climbing trips, where you might start out near freezing in the predawn light, climbing to reach the sun and finding yourself in 70-degree F midday heat. For similar yet slightly colder conditions, this layer's ability to adapt to diurnal temperature changes makes it likewise a great choice for springtime ski touring. While we praise its ability to serve you well through the spring, fall, and winter, for summer adventures, we suggest opting for a lighter-weight base layer.
Even though the SmartWool Merino 250 scores highly in terms of warmth, don't discount it when it comes to breathability, either. For its weight — and particularly in colder temperatures — this layer does a fantastic job keeping you from overheating. Merino wool is known for its natural moisture-wicking ability, and the performance of the Merino 250 is very much the rule rather than the exception. When you're working hard, this layer also kicks into high gear, pulling sweat away from your body. Thanks to the thick, 100% Merino knit (which is also naturally hydrophobic), that wicked moisture stays on the surface where it can evaporate.
All of that efficiency serves to keep you warm and dry, even when you're climbing hours in the skin track in sub-freezing temperatures. While the Merino 250 is a warm, thick, winter-focused layer, the most breathable models we tested are the thin, lightweight, summer options. Breathability tends to trend opposite to warmth, so while this layer is far from the most breathable option in our review, it still does a fantastic job for its weight class. Its balance of warmth and breathability are what truly makes this a stand-out base layer.
Comfort and Fit
The Merino 250 is the type of base layer you never want to take off. You may find yourself waking up in it, wearing it out all day on the mountain, out to dinner in the evening, and then back to bed — we know we've found ourselves in this very situation. The uber-soft, plush 100% Merino wraps you up like your favorite blanket, and is designed with mobility in mind. So no matter the activity, you will likely find yourself reaching for this ultra-versatile top.
A simple yet elegant construction is sewn exclusively with flatlock seams, so that there is no rubbing when worn next-to-skin. The Merino 250 sees a thoughtful update to its shoulder seams. By increasing the width between the offset shoulder seams, it is now much more friendly to those with broader shoulders. Even though such a simple change in design might appear arbitrary, we found this updated version much more comfortable to wear with a heavy pack. Even though this layer lacks underarm gussets, the stretchy weave ensures that this top moves with you, staying in place even when stretching and straining for that next climbing hold.
The fit does run on the large side for a base layer. Particularly if you really wear it out between washings, a size medium fits rather loose on the 5'10", 155lb, slender mountaineer's frame of our head tester. While the longer torso is nice for tucking in, we often find ourselves pushing up the longer sleeves when cooking or eating. Over time, we have decided that we love this slightly larger fit for its versatility as a casual top or mid-layer. But if you want this to fit tightly as a base layer, or are in-between sizes, we might suggest sizing down.
It may come as little surprise that the Merino 250 does not excel in drying out quickly. Our soak and dry test simulates hand-washing and flat-drying, much like you would do on a backpacking trip. So if this is going to be one way you use this base layer — and based on versatility, we think it is a great layer for multi-day trips — just make sure to give yourself an hour or more to ensure that this top is thoroughly dry. That said, it's not the only top in this review to dry slowly, and even dries faster than some competitors of lighter weight fabrics.
After soaking this top in our timed drying speed test, the Merino 250 proved to not be the fastest at drying out. Being on the thicker side of the fabrics tested, we weren't necessarily surprised by this result. That said, it's not the slowest and even dried quicker than products with thinner fabric. And although it was slow to dry after being completely soaked thru, this top does a great job of wicking sweat and staying dry when being worn. It will just take a long time to dry when you jump in that alpine lake with it on. Being made of wool, this top still insulates when wet; it just doesn't feel all that nice.
This test provides insight into how efficiently a base layer dries after wicking up a sweat, but it doesn't paint the full picture. When worn, the Merino 250 does a fantastic job of efficiently wicking up and quickly dispersing sweat to the outside of the fabric, where it can evaporate easily. As we mentioned before, Merino wool is naturally hydrophobic, so this top resists absorbing moisture. From the outside, that means that it will still insulate even when wet, just in-case you get caught out in a rainstorm. From the inside, that means sweat will wick and evaporate away without this layer soaking through.
Merino wool is nearly unmatched in its warmth and breathability — not to mention its natural tendencies to regulate temperature, wick-away sweat, insulate when wet, and resist odor. But durability may be this super-fabric's Achilles' heel. The thick weave is the one-saving grace of the Merino 250, at least when directly compared to other Merino layers in this review. The high-quality construction, including heavy-duty flatlock stitches, has led to some testers wearing this top for multiple years of outdoor use.
Even after our abrasion test, this top only showed minor surface scarring, while other similarly weighted Merino tops completely wore through. For those wearing this layer externally for rough activities like climbing or biking, you can expect the inevitable wear-and-tear. But ironically, improper washing and drying are more likely to be the death of this garment. Fortunately, Merino is naturally anti-microbial (i.e., resistant to odors), which means most of us can get away with wearing this top more and washing it less.
Although SmartWool claims this product is dryer-safe on a low setting, we suggest flat drying all Merino wool products. As a natural fiber, Merino wool is still considered delicate, and the dryer will be your fastest route to a base layer wearing out.
We love the versatility of the SmartWool Merino 250 as a top that can be worn next-to-skin just as easily as it can be worn as a mid-layer over a thin base layer. Regardless of how you organize your first few layers, this top is as comfortable under an insulated jacket or a mid-layer — on really cold days, we couple the Merino 250 with our favored Patagonia R1 Hoody for supreme warmth.
For as thick as this fabric is cut, it layers well under almost anything. In fact, we have yet to wear this top in a way that feels bulky or restricts movement. The natural elasticity of Merino resists bunching, even when worn under a notoriously sticky mid-layer like the R1.
The Merino 250's handsome appearance means it's totally acceptable to our testers to wear around town. We continue to receive compliments on its sleek fit, which is in no way overtly athletic. The looser fit compliments wearing it casually over a t-shirt — it is as appropriate to wear this layer through sweater-weather as it is in the depths of winter.
We're not going to pull the wool over your eyes on the price; the Merino 250 carries a price tag that complements its quality. But based on its performance and versatility, there are few other options we tested that present such an incredible value. Follow the care instructions and treat it well, and this might be the only base layer you have to purchase this season.
We have tested many great base layers over the years, but there are few that balance high quality and high performance like the SmartWool Merino 250. Time and again, this is an easy choice for our Editors' Choice Award based on its ability to blend warmth, breathability, comfort, and versatility seamlessly. While other tops may score higher in specific metrics, none quite compare to this 3-season, do-everything layer. From ski bums to business professionals, this top earns its place in every wardrobe.
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