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SmartWool Merino 250 Bottoms Review

An extremely warm and breathable pair of bottoms built to keep you warm in the coldest conditions but versatile enough to carry into seasons outside of winter
Top Pick Award
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Price:  $100 List | $69.93 at REI
Compare prices at 3 resellers
Pros:  Extremely warm, super cozy, terrific temp regulation, breathable
Cons:  Stretches out between washing/drying cycles, saggy crotch, slow to dry, expensive
Manufacturer:   Smartwool
By Roland Mott ⋅ Review Editor  ⋅  Nov 19, 2019
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#3 of 9
  • Warmth - 30% 9
  • Breathability - 30% 6
  • Comfort and Fit - 30% 7
  • Durability - 10% 7

Our Verdict

The super cush and thick merino wool of these long underwear bottoms is meant to keep you warm in the coldest climates and earns our Top Pick for warmth. The SmartWool Merino 250 Bottoms are perfect for those adventuring into the deep recesses of winter, or people working in really cold conditions. The 100% Merino fabric insulates like a furnace but breathes wonderfully, making this layer really versatile — performing in super cold conditions but not forcing you to overheat when you get into warmer situations. A workhorse bottom layer, this kept us warm skinning ridgelines and ice climbing alike.

While its performance is top-notch and comfort-level is through the roof, this layer doesn't fit quite as we expected. Comfortably snug through the legs, but we couldn't get the seat right without pulling the waistband almost up to our belly-button — otherwise, we ended up with some saggy-butt. Otherwise, we love the balance of warmth and versatility in this layer. But if your activity is more often highly aerobic, it may be worth checking out the Smartwool Merino 150 bottoms — practically the same layer, just built at a slightly lighter material weight.

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Our testers are big fans of the SmartWool Merino 250 top, which won our Editors' Choice Award in our base layer tops review.

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Our Analysis and Test Results

Our Top Pick for Warmth, the SmartWool Merino 250 balances insulation built for really cold climates with comfort and breathability. That combination puts it at home in a sideways-blowing blizzard, and for a day of reading and movies lounging around the cabin.

Performance Comparison

The ultra cush  thick and cozy fabric of the 100% merino 250
The ultra cush, thick and cozy fabric of the 100% merino 250


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.

The naturally hydrophobic fibers of Merino wool resist absorbing sweat, which allows for warmth and comfort throughout a full day of varying intensity of activities and temperatures. These bottoms were glued to our burning thighs on the 6,000 vertical feet of skinning and climbing to reach the summit of Mt. Hood in the heart of winter. From frigid, windy pre-dawn temps to the double-digit afternoon and into the cold, dark night, these bottoms kept us warm, dry, and happy the whole time! They are warm but not expedition weight warm, if you're heading to the coldest regions on earth, you will need something thicker.

Nearing the summit of Hood.
Nearing the summit of Hood.


What makes these bottoms so impressive beyond their comfort is their ability to provide such incredible insulation while maintaining a healthy ability to breathe. This combination is not easy to find. A lot of times, a thick and warm fabric will do great in cold situations, but once you start working hard, they will cause you to overheat and will hold onto sweat, becoming clammy and lending itself to cold once you stop moving. The Merino wool naturally wants to repel water and does an excellent job at wicking sweat away from the skin and using the pressure/temperature variance between your skin and the air to dry quickly, so you're not left with clammy or sweat-soaked bottoms.

The uncanny ability of merino wool — and these bottoms specifically — to deliver maximum heat as well as maximum breathability is like striking gold! Although its breathability is impressive for its weight and warmth, it is not going to breathe as well or efficiently as it's thinner partners. If you are looking for a base layer to double as running leggings, or often strike out on the skin track at a skimo-pace, we suggest checking out some of the lighter-weight options in our review.

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

These bottoms — just like all Merino wool fibers — are naturally hydrophobic, so it takes quite a bit of effort to soak them through. Once they are soaked through, however, they are heavy and slow to dry. Situations where you are wearing base layers that are soaked all the way through are hopefully rare, unless you're accustomed to jumping into lakes with your long-johns on. In the drying test, it was not surprising that these were the slowest to dry, as they are the thickest bottoms we tested.

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

Comfort & Fit

These bottoms are heavenly when it comes to comfort. SmartWool's 250-weight merino has won over the hearts of everyone here at OutdoorGearLab. The fabric is thick, soft, incredibly stretchy, and super warm. We don this fabric the "Cadillac of Cush." When it comes to fabric comfort, these bottoms are the creme-de-la-creme, and second to none! They fit snug against the skin but are not itchy at all. The stretchy fabric allows the ankle of the pant to slide over the heel easily and fits both thick and thin legs well. Even though they are made of a thick fabric, they layer well under ski pants and jeans alike.

Here's the fit of the Merino 250 bottoms on our 6' lead tester.
Here's the fit of the Merino 250 bottoms on our 6' lead tester.

A minimalistic design allows for a single seam to run the length of the leg on the inseam instead of two. Flatlock seams sit comfortably against the skin, and a gusseted crotch allows for unrestricted mobility. The waistband deserves its own review! It is by far the most comfortable waistband we tested. The waistband is not a separate material from the pant — it is the same comfortable Merino on a flat, wideband that lays comfortably on the waist. The only room for improvement that we observed is in the crotch. When worn at a respectable place on the waist, there is a bit of crotch sag. For the crotch to fit correctly, we found that we had to hike them up just beyond our belly button.

The uber-comfy waistband of the SmartWool Merino 250
The uber-comfy waistband of the SmartWool Merino 250


Being the thickest merino layer, these are easily among the most durable merino layers we tested. Nearly all of the merino 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 the breathability, wicking capabilities, and non-stink that only Merino can promise.

The soft material can tear easily if it is snagged on sharp edges and develops holes in high use areas after extended use and abuse. As with all Merino, washing — and especially drying — dramatically decreases the life of a Merino garment. We suggest washing these only when you need to and laying them flat to dry. All that said, of the Merino options on the market, these are some of the most durable.

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


This is one of the most expensive pairs of bottoms in our review, but we feel that the quality and versatility of the product warrants the price. All Merino layers are expensive, and the other top performing layers in the review are only slightly less money.


All in all, the SmartWool Merino 250 bottoms offer a great balance of warmth and breathability in an ultra-comfortable package. They are a great investment for those needing a pair of bottoms for very cold weather but wanting a layer that isn't stuck working in only freezing conditions.

Roland Mott