SmartWool Merino 250 Bottoms Review

Picking up a redesign for this season, the SmartWool Merino 250 Bottoms now incorporate a gusseting pattern in both the front and back for a fit that is both more functional and more comfortable. No longer do you have to size down to achieve the proper athletic fit for these base layer bottoms.

Performance Comparison

Nearing the summit of Mt Hood.

Photo: Roland Mott

Warmth

Constructed to excel in harsh winter conditions, the Merino 250 Bottoms boast a fabric weight of 250 g/m², the heaviest in SmartWool's lineup. The 100% Merino wool is thick cut, making these bottoms much more plush feeling next-to-skin than comparably weighted models we tested. These pants are plush, an ideal companion for full days spent outside through the coldest months of winter.

Boasting 250 g/m² of thick and cozy 100% merino wool, these bottoms are constructed to excel in harsh conditions. They do a superb job of wicking away sweat when you're working hard and drying quickly against your skin so that after skinning endlessly for the perfect line, you're not soaked and freezing when you finally reach the windblown and frozen summit.

Tough like the summit winds, the thick fabric of the SmartWool Merino 250 is by far the most durable merino bottom we tested.

Photo: Roland Mott

Merino wool is naturally hydrophobic, which keeps these base layer pants warm and comfortable throughout the day, regardless of how intensely you are working up a sweat. The thick Merino wool traps just enough heat to allow this layer to dry against your skin quickly. Even through 6,000 vertical feet of skinning and climbing to reach the summit of Mt. Hood on a mid-winter ascent, the Merino 250 bottoms were warm and dry by the time we reached the summit—even if we weren't in the frigid alpine wind. It is important to mention that while these bottoms are warm, they are not expedition-weight warm. So if you're planning a trip north of the Arctic Circle, plan on buying something even thicker.

Even if you have to eventually get out your bag in the morning, these bottoms are a great bet to keep you warm and cozy.

Photo: Jill Rice

Breathability

What continues to impress us about these bottoms is how aptly they balance top-notch insulation with near top-notch breathability. Functional thermoregulation is not a common-trait amongst base layers, and the Merino 250 bottoms handle that task masterfully.

The special interlock knit used in the design of these bottoms sets the scene for breathability of this thick layer and truly helps set the Merino 250 Bottoms apart from the competition. The lattice-like knit adds additional loft, supplementing the natural breathability of merino wool fibers with a microclimate that uses heat to force moist air up through the fabric, where it is able to evaporate on the surface. Unlike other thick layers that hold onto sweat and become clammy once you stop moving, these avoid becoming sweat-soaked by harnessing the power of simple thermodynamics—the harder you work, the more powerful the temperature/pressure gradient between your skin and the outside air, and the faster these bottoms dry out.

Seeing how our thickest pair of bottoms does when the sun warms things up a bit on a fall river trip.

Photo: AJ Wojtalik

We generally consider merino wool to be an all-natural super-fiber, one that wants to insulate, breath, and moisture-wick all at once. But if they happen to soak-through, it is important to mention that these bottoms will take a long time to dry out. Plan taking more than an hour for this layer to flat-dry in the sun. Although the breathability of the Merino 250 Bottoms is unmatched for their weight and warmth, they will certainly not breathe nearly as well as thinner models we tested.

Nearing the end of the skinning slog and getting excited to put on crampons! Mt. Hood, OR

Photo: Adam Zagorski

Comfort & Fit

The Merino 250 Bottoms have effectively won over the hearts of all of our testers — when it comes to pure comfort, these bottoms are heavenly. Not only are they warm and cozy, but the 100% Merino knit is thick, soft, and stretchy. SmartWool designers seem to take this fact with pride, and this updated version thoughtfully lines the interior of the extra-wide waistband with Merino wool to increase comfort further and cut down on a common spot for irritation. The entire construction is supported by flatlock seams that are specifically designed to minimize rubbing and chafing, giving you even more reason to wear these bottoms directly next-to-skin.

We often wear these truly as long underwear, opting to comfortably layer them under our jeans during the coldest months of winter. The natural elasticity of Merino wool makes these bottoms a versatile option to prepare for those extra-cold moments, like freezing your buns off in an ice-climbing belay stance. The material is stretchy enough to pull over a lighter weight base layer, and yet somehow snug-enough fitting to wear below a mid-layer pant without any constrictions.

Our lead tester is 5'10", 155lbs, wearing a size medium. You will notice some sag in the seat, but we promise, it's not the pant's fault.

Photo: Jill Rice

A minimalistic design incorporates a gusseted crotch, allowing for a single seam to run the length of the inseam without losing out on flexibility. While we dealt with saggy-bum issues in the past, this update takes the same gusseted design from the front and applies it to the back of the pants. Now you don't have to pull these bottoms up past your belly-button to secure a snug fit.

Comparing the thickness of the merino wool-lined waistband on the SmartWool Merino 250 bottoms (right) to other models we tested.

Photo: Jill Rice

Durability

While merino wool is reputed to have durability issues, modern knitting and design technique has done a seriously great job of improving upon concerns. The SmartWool 250 bottoms are the thickest Merino layer in our review, easily landing them among the most durable all-natural options we tested. Even after our overly aggressive abrasion test, this pant exhibited mere surface wear. Still, for snags and punctures, they will simply not be as durable as other synthetic options.

Being the thickest merino wool layer, these are easily among the most durable wool layers we tested. Nearly all of the merino wool bottoms developed a hole during our abrasion test, whereas these boasted mere surface wear. As they are merino wool, they are just simply not as durable as some synthetic fabric. Still, they offer breathability, wicking capabilities, and resist odor build-up very well.

A hanging tab is a nice touch for air-drying, and keeps these bottoms from getting stretched out in a weird way.

Photo: Jill Rice

The main way you can protect your purchase and invest in the longevity of a Merino base layer is through proper laundering. By carefully washing, and most importantly, flat drying, the Merino 250 Bottoms, you will likely have these are your go-to cold weather bottoms for years. While you may experience them stretching out between washings, don't feel inclined to shrink them up in the dryer — that is the surest path to an early grave for this high-quality layer.

Full flatlock seams keep itchiness at bay.

Photo: Jill Rice

Value

Although the Merino 250 is one of the most expensive pairs of long underwear bottoms we tested, the quality of construction and sheer ability to balance warmth and breathability warrants the price tag. Think of it as an investment in your well-being, to keep you warm, dry, and performing your best even through frigid conditions.

Nothing quite beats the all-natural abilities of 100% Merino wool. We also appreciate that this tag is designed to be cut off (once you memorize the care instructions, of course.)

Photo: Jill Rice

Conclusion

The SmartWool Merino 250 Bottoms offer superb warmth and thermoregulation, wrapped up in an uber-comfortable package. For those that need an extra boost of warmth to get them through the winter, these are a great investment that will prove themselves worthwhile even after the mercury rises from sub-freezing temperatures.

From the high alpine to your next backpacking trip, these versatile bottoms are sure to be a constant companion on many outdoor adventures.

Photo: Jill Rice