Smartwool Merino 250 Base Layers Review

I tested the Smartwool Merino 250 crew and bottom and this is my verdict.

October 12, 2022
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The Smartwool Merino 250 base layer crew and bottoms are a favorite for layering when the temperature drops. Soft, stretchy, and very comfortable, this merino wool crew neck long sleeve and leggings combo is the best at temperature regulation and insulates even when wet.

Product Overview

Smartwool Merino 250 Thermal Base Layers - Crew

smartwool merino 250 crew

Smartwool Merino Thermal Base Layers - Bottoms

smartwool merino 250 bottoms

✅ Comfortable

✅ Warm

✅ Great fit

✅ Odor-resistant

✅ Not itchy

✅ Flat-lock seams

✅ Gussetted crotch


❌ Heavier than some base layer bottoms


  • Material: 100% Merino Wool
  • Weight: Crew: 9.7 oz (0.6 lbs) Bottoms: 8 oz (0.5 lbs)
  • Fabric Weight: 250
  • Flat Seam?: Yes
  • Inseam Length:
    • Small: 30-31”
    • Medium: 31-32”
    • Large: 32-33”
    • X-Large: 33-34”
    • XX-Large: 34-35”

The Smartwool Merino 250 base layer crew neck long sleeve and leggings are the foundation of an effective cold-weather layering system. At 250 grams per square meter of wool, these are the thickest merino wool base layers that Smartwool makes. These thermal layers are some of the best at regulating temperature. Wool is warm, breathes well, and maintains its insulating properties when wet.

All this makes these base layers an excellent choice for winter hiking, skiing, climbing, or other cold-weather activities. Plus, merino wool is odor-resistant, so they stay fresh even after a few days of sweating in the backcountry. These are too thick for summer base layers in most cases. I recommend a thinner weight (100-150 g/m2) base layer combo for warmer conditions.

To see reviews on other merino base layers, see our post on the best merino wool base layers.

Performance Test Results

smartwool merino 250 performance score graph

How we tested

I tested the Smartwool Merino 250 Crew and Bottoms in Colorado and Utah during late summer and early fall. I used them during a series of backpacking trips and hikes. The weather was warm, mostly in the 70s during the day and colder overnight. On one particularly cold night, the temperature dropped to the low 30s. I experienced some rainy conditions during testing as well.

Weight: 8/10

Merino wool garments are categorized by fabric density, which refers to the weight in grams per meter of fabric. The Smartwool Merino Wool Baselayer top of bottoms are both 250 weight, meaning 250 grams of wool per square meter (g/m2). 250+ is considered heavyweight. Though thicker fabric does mean the garment will be heavier, we discuss garment weight below.


I recommend merino wool base layer tops weigh between six and ten ounces. At nearly 10 ounces, this top is on the higher end of the weight range. For cold weather hiking and camping, you’ll want a baselayer top that is a bit heavier, like this one. With wool, the heavier the fabric, the thicker it will be. And thicker wool fabric insulates better.

Compared to other 250-weight merino wool baselayer tops, this crew is comparable in garment weight. There is no magic way to make a natural fiber like wool any lighter or heavier, so all 250 g/m2 garments of the same basic dimensions will weigh about the same amount.smartwool merino 250 crew

The Smartwool Merino 250 Crew weighs 9.7 oz (0.6 lbs)


I recommend merino wool base layer bottoms weighing between 5 and 9 ounces for most hiking and backpacking trips. These leggings fall into this range But again, they’re on the heavier end of the range. These base layers are probably overkill for most summer hiking and backpacking, but they’re great for the colder months or high-elevation trips. If you’re looking for summer-weight backpacking baselayer tights, something closer to 5 ounces will be sufficient.Smartwool Merino Thermal Base Layers - Bottoms

Smartwool Merino 250 Bottoms' weight is 8 oz (0.5 lbs)

Compared to other 250-weight merino wool baselayer bottoms, these are comparable in garment weight. These tights could be slightly lighter while still using 250-weight wool by using a more minimalist waistband, but that would only save a few grams at most and make these tights less comfortable.hiker wearing the smartwool merino 250 set while eating

Price: 8/10


The Smartwool crew neck offers excellent performance at a price that’s a little less than the ultra-premium models. There are also less expensive 250-weight merino wool base layer tops out there. However, Merino wool garments like this are generally comparably priced to this Smartwool top.

I believe a good wool base layer is worth the price. Wool is pretty expensive but is unparalleled in its insulating and odor-resistant properties. On a cold weather trip, you can wear this wool base layer top the entire time. Even as it gets wet, it will insulate you better than a synthetic base layer.

Also, many less expensive base layers that claim to be Merino wool might be a wool-polyester blend. These may be less expensive than a 100% merino wool base layer. Wool blend fabrics insulate relatively well but won’t be as odor-resistant.

For a 100% Merino wool base layer top, this Smartwool Crew is an excellent value. It has all the features you’d want in a base layer top without anything extra that would make it more expensive.hiker wearing Smartwool Merino 250


This base layer bottom performs really well and falls into the middle of the 100% Merino wool base layers price range. It’s not the most expensive, ultra-premium garment, nor is it the cheapest. There are less expensive 250-weight merino wool tights. However, we think these strike a good balance between quality and price.

You won’t find any 100% Merino wool tights of this quality at a lower price. On a cold weather trip, you can wear these tights the entire time. You could get away with less expensive, thinner wool bottoms on super active days. But, for cold weather, low-output activities, these tights are perfect.

For 100% Merino wool base layer bottoms, I think these Smartwool tights are an excellent value. They have all the features you’d want, without anything that would make them more expensive.hiker wearing Smartwool Merino 250

Warmth: 10/10

These layers provide a lot of warmth. As I already said, these are the warmest baselayers you’ll probably ever need. They’re warm enough to be the base layer in a winter hiking layering system. They’re also warm enough for skiing, alpine climbing, mountaineering, and other extreme-cold activities.

I recommend wearing these layers in winter, spring, and fall primarily. These base layers are perfect for any conditions where warmth is a priority.

I used this top as our main hiking layer when hiking at high elevations in the summertime. It was generally not too warm, but it got pretty hot when I went up steep hills. When the temperature is above 60 degrees, this top will be hot, even if worn alone. Wool doesn’t get as hot as some materials, but this thickness of wool is too warm for summer conditions. I recommend a thinner 100-weight base layer top and bottom combination for summer hiking.

Compared to other merino wool base layers on the market with the same fabric density, these base layers are comparably warm. They’re 100% Merino wool, some of the best wool available. They aren’t warmer than other wool garments with the same fabric density. But, no 100% merino wool 250-weight garments will be warmer than other 250-weight clothing unless they’re thicker.hiker wearing Smartwool Merino 250

Material & Durability: 9/10

The Smartwool Classic Thermo Merino 250 base layer crew and bottoms are made with high-quality 100% merino wool. Smartwool also uses ZQ-Certified merino wool, which is produced in an ethical and environmentally conscious way. The sheep raised for their ZQ-certified merino wool are treated ethically, with plenty of room to graze, shelter, and have the opportunity to live their lives as sheep normally would. Unfortunately, most sheep raised for wool aren’t treated this well.

Merino is one of the least odor-prone fabrics available. For this reason, wool is the best material for thru-hiking. After a week-long backpacking trip, your wool garments will probably smell some. But wool stays fresher than polyester, nylon, or cotton after heavy use.
hiker in camp

I wore a 100-weight Smartwool shirt on a CDT thru-hike last summer. When I compared the smell of my Smartwool shirt with the polyester fleece I also wore, the wool always smelled better. After wearing the same 100-weight Smartwool shirt for over 2000 miles last summer, it has some holes where my backpack rubbed on my lower back. Other than those wear areas, the shirt is still going strong.

After many washes and wears, these base layers still seem as they did when they were new. Merino wool is less durable than synthetic fibers. However, it is still very durable. Also, since these base layers are a thicker wool, they will last longer than a thinner 100-weight wool shirt.

waistband of the smartwool merino 250 bottoms

These base layers are just as durable as other 100% merino wool garments from other brands. I’ve seen wool-polyester blend shirts last slightly longer than 100% merino does. But, I think the benefits of 100% wool outweigh the somewhat lower durablility.

Also, wool is much easier to recycle, and Smartwool has started a program to recycle old wool socks. I hope this program expands to include other old wool garments soon.smartwool merino 250 crew

Comfort: 10/10

These are some of the most comfortable base layers I’ve ever worn. This is especially true when wearing them with a backpack and underneath pants. All seams on these base layers are flatlocked, so there isn’t extra fabric sticking out that will chafe against your skin. They stretch enough to work for any activity, and the material is soft and comfortable.

The crew has a shoulder panel sewn onto the top of each shoulder, so backpack straps don’t rub the seam underneath. This is a minor detail, but little details like these make this crew very comfortable.hiker climbing while wearing the smartwool merino 250 set

The Smartwool Merino 250 Crew and Bottoms are very comfortable even when climbing. No chafing at all.

Similar to the shoulder panels, the back panel of this crew is wider at the bottom than the top. This makes the back panel wrap around the front of the shirt, angling forward from the armpits. The side seams of the shirt don’t chafe on the hips because of this.

The only thing about these base layers that isn’t comfortable is the tags. I highly recommend cutting off all the tags first thing. They are by far the itchiest part of these base layers.tags

We found the tags itchy and uncomfortable... we suggest you cut them off before you wear the Smartwool Merino 250 Set.

Fit & Layering: 10/10


This is the best-fitting 250-weight merino wool base layer shirt I’ve worn. This crew fits just as it should for easy layering. The small top I tested fit tight but wasn’t too snug. It’s just tight enough to make pulling other layers over the top a breeze.smartwool merino 250 crewIt’s also stretchy enough to work as a mid-layer over another base layer. I think a great layering system for a chilly day of hiking would be a wool t-shirt, this crew, and a light windbreaker or rain shell.layering the smartwool merino 250 crew

Layering the Smartwool Merino 250 Crew


These merino base layer bottoms fit very well, like the crew top. They’re tight enough to layer over. And, they move with you if worn underneath pants. They’re also stretchy enough to wear over another pair of tights, but this will be too warm in all but the coldest conditions.layering the smartwool merino 250 set

Layering the Smartwool Merino 250 Set

Compared to other merino wool base layer bottoms, these fit better. I didn’t know what I was missing until I tried these compared to my old wool base layer tights. These are the only base layer tights I’ve seen that feature a gusseted crotch. Even though wool is relatively stretchy, and this gusset might not be necessary, it makes the fit that much better.gusseted crotch

Having a gusseted crotch is one of our favorite features of the Smartwool Merino 250 Bottoms

Breathability: 10/10

These base layers are highly breathable. Merino wool is a very breathable material. If you’re wearing these base layers on their own, you will feel the wind. However, this also means your sweat will evaporate through the shirt as you heat up. Compared with other merino wool base layers, these breathe as well as the best.breathability

Drying: 8/10

One of merino wool’s biggest weaknesses (maybe its only weakness) is drying time. These base layers, like all merino wool clothing, take longer to dry than synthetic fabrics. However, if you lay these base layers out in the sun, they will dry quickly enough. I usually leave them on and allow my body heat to help dry them off, but they also have hang loops for drying. One of the most significant benefits of merino wool is that it doesn’t make you as cold when it’s wet compared to cotton or synthetic materials. So, I simply leave these baselayers on and let them dry on my body.drying

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About Sam Schild

By Sam Schild (aka “Sia,” pronounced sigh): Sam is a writer, thru-hiker, and bikepacker. You can find him in Denver when he’s not out exploring in the mountains somewhere..

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