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Smartwool Merino 150 Base Layer Bottoms - Women's Review

A lightweight option with superior breathability but a list of caveats
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Price:  $85 List | $55.25 at Amazon
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Pros:  Lightweight, excellent wicking power, durable fabrics
Cons:  Very tight and unforgiving fit, waist slides down, not warm
Manufacturer:   Smartwool
By Amber King ⋅ Senior Review Editor  ⋅  Nov 17, 2020
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66
OVERALL
SCORE


RANKED
#9 of 10
  • Warmth - 30% 6
  • Breathability - 30% 9
  • Comfort and Fit - 30% 4
  • Durability - 10% 9

Our Verdict

The Smartwool Merino 150 stands out for its lightweight architecture and superior wicking power. In the past, it's been a favorite for its performance in aerobic sports, ranging from backcountry skiing to cold winter running. While it still boasts these high scores for thermoregulation, the latest iteration has a new waistband that demotes its comfort and fit rating. The waistband feels small in circumference, and any woman with a little extra meat on the thighs or hips will have a heck of a time wiggling into them. If you do decide to buy them, we recommend considering sizing up an entire size to enjoy its lightweight and durable performance.

Compare to Similar Products

Our Analysis and Test Results

The Smartwool Merino 150 stands out as a lightweight and durable merino-synthetic blend with a tight, unforgiving fit. It's constructed of 87% merino wool and 13% spandex. This product saw an update in 2020 that changed its waistband, which significantly changed its comfort and fit rating. While we'd recommend it for most activewear sports, it's important that you size up. If you're sensitive to wool, we wouldn't recommend it as we notice the fabrics are itchier than any other contender tested.

Performance Comparison


We enjoy the wicking and breathing performance of these pants. We just wish the fit was a touch bit stretchier and not as tight.
We enjoy the wicking and breathing performance of these pants. We just wish the fit was a touch bit stretchier and not as tight.

Warmth


As a lightweight merino-synthetic blend, this long underwear pant offers activewear warmth in the winter that would work best with a pair of insulated pants. It contains 150 g/m² of material, making it one of the lightest options tested. The fabric weave is surprisingly tight, so while it is thin, it still provides some protection when worn on its own for cutting wind and insulating. If running, cross-country skiing, or uphill hiking is on your agenda, this pant is a great one to choose. Not because it's super warm, but because it'll breathe and wick exceptionally well to keep you dry. If you are at the resort, however, this isn't the option that we'd recommend as it doesn't insulate well during long cold periods of sitting around. For use throughout the seasons in cool weather or while exercising, it does provide all the warmth you need.

In cold weather  this is an excellent choice for running  cross country skiing  or any other aerobic activity on its own. It also pairs well with a pair of pants for a little added warmth while hiking or skiing.
In cold weather, this is an excellent choice for running, cross country skiing, or any other aerobic activity on its own. It also pairs well with a pair of pants for a little added warmth while hiking or skiing.

Breathability


This layer has excellent breathability because the fabric is so thin. While it insulates, it is able to easily move moisture away from the skin. The weave of the fabric is fairly tight, unlike other heavier Merino wool options without a synthetic component. As a result, the thin fabrics make up for the tight weave, earning it a similar score in breathability as other options that are supposedly warmer and thicker. This is a great choice for aerobic activities in cold weather or to wear in warmer climates.

A look at the fabrics when held up to the light. The materials are quite thin and almost a little see-through.
A look at the fabrics when held up to the light. The materials are quite thin and almost a little see-through.

Comfort and Fit


This pant used to be a favorite for its excellent performance and comfortable fit. However, the newest iteration has changed the fit completely, even though the material specs seem to the same. It feels incredibly tight and rigid without much give or stretch. We ordered a size medium, tried it on, and immediately sent it back, thinking that we had received a lemon. However, when we got another version in the mail, we had the same issue.

The fit of a size medium. Our tester is 145 lbs  5'7 and normally fits a medium pant. According to our pool of testers  this feels tighter than usual.
The fit of a size medium. Our tester is 145 lbs, 5'7 and normally fits a medium pant. According to our pool of testers, this feels tighter than usual.

Our tester who fits a medium in all the pants in this review could hardly get into this pant, wiggling and stretching the fabrics to the max. Thinking that we'd eaten a little too much candy this Halloween, we handed it off to other women that normally fit a size medium, and got similar feedback.

A look at the fit to the side. It's also important to acknowledge that it doesn't reach all the way through the ankle. Our main tester has legs average in length for her height.
A look at the fit to the side. It's also important to acknowledge that it doesn't reach all the way through the ankle. Our main tester has legs average in length for her height.

Smaller friends who fit a size small said the medium felt good for them, but most still didn't like the itchy feel of the fabrics and the rigidity of the new waistband. There are many other lighter-weight options that have a fit with more versatility that doesn't stretch out.

The materials are light with a tighter fit. The waistband has seen an update in this iteration. While it's a good thought  we wish it was a touch bit stretchier.
The materials are light with a tighter fit. The waistband has seen an update in this iteration. While it's a good thought, we wish it was a touch bit stretchier.

All of our testers agree that this isn't one we'd buy because of this issue. However, of the contenders, it's the one that won't stretch out even after wear for several hours. If you do buy this model, be sure to size up if you need a little extra stretch around the waist and hips.

Durability


With the integration of synthetic fibers to uphold the shape of the fabrics, this piece proves to be durable. After wearing it on its own while hiking and running, we see next to no wear and tear so far. There's no pilling to speak of, and the fabric hasn't stretched out or deformed. While the fit is rigid, it has its upsides. Of the merino wool options out there, this one surpasses others in this metric, earning it top marks.

The merino-synthetic blend is surprisingly durable.
The merino-synthetic blend is surprisingly durable.

Value


If the fit works for you, this is a great value option with excellent durability that we've seen in our testing. As a merino-synthetic blend, the fibers are hard as nails and typically do a great job when it comes to longevity, assuming the pant isn't completely abused. While it's not the highest value option out there, it's still a lighter base layer that has incredibly wicking and breathing power. If that's what you seek, be sure to size up to enjoy it while playing in the great outdoors.

Conclusion


The Smartwool Merino 150 is a lightweight merino-synthetic base layer that offers superior breathability and wicking power. It's surprisingly warm for its thin fabrics and is best used for aerobic activities in cold weather. Unfortunately, the waistband is tight with an unforgiving fit. If you buy it, be sure to size up one full size for a little extra stretch, unless you prefer skintight performance.

Getting ready to descend into the Ouray Ice Park for some ice smashing. We wear the Smartwool 150 layered nicely underneath our soft pants. These pants have a little fleece insulation which makes these base layer bottoms a great choice for this activity.
Getting ready to descend into the Ouray Ice Park for some ice smashing. We wear the Smartwool 150 layered nicely underneath our soft pants. These pants have a little fleece insulation which makes these base layer bottoms a great choice for this activity.

Amber King