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Smartwool Classic All-Season Base Layer Review

Adam Sanders
Paul Sozio bio photo
ByMultiple Authors
Jan 22, 2026
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Our Take:
4.3/5

The Smartwool Classic All-Season ($100 for the crew version) is a lightweight, majority merino base layer that excels at everyday adaptability. It’s soft, odor-resistant, and warm enough for shoulder-season use or as a ski layering system, but it shows its limitations during high-output activity (compromised breathability) and deep-winter freezes (lightweight warmth). Thin fabric keeps weight down but also shortens its lifespan; this is a dependable, do-it-all layer—it just might develop holes quicker than you’d prefer.

Warmth

Warmth

3/5
Breathability

Breathability

3/5
Durability

Durability

2.5/5
Comfort

Comfort

4.5/5
Odor Resistance

Odor Resistance

4.5/5
Sustainability

Sustainability

3.1/5

Fabric(s)

88% merino, 12% nylon

Fabric weight

150 g/m²

Weight

6 oz.

Variations

Crew, quarter-zip

Pros

Versatile across a range of temperatures and activity levels.
Has all the benefits of merino: soft, odor-resistant, and warm for the weight.
Available in a wide assortment of colorways, in addition to crew, quarter-zip, and short-sleeve designs.

Cons

Thin merino will wear down over time, forming thin spots or holes in high-use areas.
Not our first choice for high-output activity; merino can easily overheat and is slow to dry.
Not warm enough for true winter temperatures.

For this season's top models, see our guide to the Best Base Layers.

The Smartwool Classic All-Season is a light-to-midweight base layer, sitting below the Classic Thermal and Intraknit Thermal in Smartwool’s lineup. Its 150-gram fabric, made from 88% merino wool and 12% nylon, is noticeably thinner than Smartwool’s Classic Thermal (250-gram) and only slightly thicker than lightweight synthetic base layers like The North Face Summit Series Pro 120 (120-gram). I found the All-Season most comfortable when temperatures were in the 30s to 50s and when worn under a light insulating layer like the Arc’teryx Atom LT for hiking and backpacking, or beneath a windbreaker for running.


I used the Smartwool Classic All-Season for hiking, trail running, backpacking, and both resort and backcountry skiing. When touring, I wore it under a Patagonia R1 fleece; in the resort, with temperatures in the 20s and 30s, I layered it under an insulated shell. For lower-output lift-serve skiing, it worked well, but while backcountry skiing, it absorbed sweat quickly and felt cold once I stopped moving. While merino technically retains warmth when wet, it also retains moisture more than polyester. Personally, I don’t love midweight merino for highly aerobic winter sports. Contrary to its name, the All-Season’s warmth is appropriate for shoulder season and moderate output, but it’s not a winter specialist unless you’re keeping your heart rate fairly low.

The Classic All-Season’s breathability is adequate, but very situational. When worn on its own or under a light insulating layer that promotes good airflow, it manages moisture reasonably well. However, once you add a pack, a running vest, or a hardshell, sweat buildup becomes noticeable—especially in humid conditions or during sustained output.


Merino’s natural moisture management helps initially, but once saturated, this layer dries slowly and can feel clammy. I found that trait most problematic while backcountry skiing, when I consistently overheated on the climb and then felt chilled during transitions. Compared to heavier merino base layers, the All-Season does breathe better, but it still can’t match the wicking properties of a synthetic base layer like The North Face’s Summit Series Pro 120 during intense cardio. For moderate hiking or cool-weather runs (think in the 40s and 50s), it’s fine, but for all-day aerobic output, it’s not ideal.

There’s no getting around the reality here: Thin merino wears out quickly. The All-Season’s 150-gram fabric is lightweight and comfortable, but it’s prone to thinning and eventually will develop holes in high-wear areas like the elbows, cuffs, hems, and underarms. Its 12% nylon content helps slow that process, and Smartwool’s construction is high quality, but it won’t prevent wear altogether.


At $100, it’s priced competitively for a premium merino base layer, but there are alternatives that offer thicker fabric and potentially better longevity for less money. For example, the Ridge Merino Aspect (84% merino, 16% nylon) is slightly thicker at 180 grams per square meter, has more nylon content, and is cheaper at $80. The All-Season feels like a piece that’s meant to be used often and replaced semi-regularly, rather than a long-term workhorse. It is, however, a bit more durable than 100% merino options like the Ortovox Rock’N’Wool (185-gram) thanks to its nylon blend.

Comfort is the Smartwool Classic All-Season’s strong suit. Out of the box, it felt slightly scratchy, but after one wash and hang-dry, it softened significantly. Against the skin, it’s smooth, stretchy, and form-fitting without feeling restrictive. The fabric moves well with my body, making it comfortable for long days of wear across multiple activities.


Compared to budget merino base layers, Smartwool’s material has a noticeably silkier handfeel and less itch, even during extended wear like a full day on the slopes. It fits close to the body, as a base layer should, but retains enough give that it never feels oppressive. As a next-to-skin layer, it’s one of the more comfortable merino options I’ve worn.

Despite the All-Season’s nylon content, odor resistance is excellent—almost as good as you’d get from pure merino. After multiple days of skiing both at the resort and in the backcountry, without washing, the All-Season remained remarkably stink-free. That’s a stark contrast to synthetic base layers, which often smell even after laundering.


For multi-day trips where washing isn’t an option, this is a major advantage. The merino-heavy fabric behaves exactly like a traditional wool base layer in this regard, making it a strong choice for travel, backpacking, and hut trips where you’re likely sweating up a storm and not rotating through a whole lot of costume changes.

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Longevity

Choosing durable outdoor gear and keeping it in use for longer is one of the best ways to reduce environmental impact. Our proprietary longevity rating assesses factors like overall build quality, materials, fabric denier, component durability, and real-world performance. A green check indicates that we expect the product to be long-lasting relative to its peers, a yellow check mark indicates average longevity, and a red X indicates a product that may have a limited lifespan.

Tester: 5’9” 155 lb.

Size tested: Men’s small

The Smartwool Classic All-Season’s fit is slim and true to size, with good stretch throughout. It’s snug enough to function properly as a base layer but doesn’t straightjacket you. I found that it was not as form-fitting as something like The North Face Summit Series Pro 120, but it rather hugs the body while leaving a little room to breathe. I’d recommend sizing normally and wearing it strictly as a next-to-skin piece rather than trying to use it as a standalone midlayer.

Smartwool Classic Thermal ($125): Merino Heavyweight
The Classic Thermal is the All-Season’s heavier, full-blooded merino cousin. Its 100% wool, 250-gram material makes it more of a cold-weather specialist, and it’s even softer and more luxurious-feeling than the All-Season. The Classic Thermal is among the warmest base layers we’ve tested, but that makes it less versatile than the All-Season. You can quickly become too warm in it in mild conditions, and you’ll probably boil over even in arctic temperatures if you’re working at a moderate pace. The Thermal is better as a resort skiing layer or an in-camp piece for winter overnights, but for the rest of the year, we’ll take the All-Season. To learn more, check out our Classic Thermal review.


Ridge Merino Aspect Midweight ($80): An Affordable Standout
With its 180-gram fabric weight and 84% merino, 16% nylon blend, the Aspect is both slightly warmer and slightly more durable than the All-Season. It also boasts thumb loops and a longer cut. Use-wise, the slightly heavier Aspect falls more on the cold-weather side of versatility, but neither base layer is cut out for standalone wear in deep winter conditions, or as an active piece if you’re dialing up the RPMs. Those who want soft comfort to be the defining characteristic of the base layer might want to go with the All-Season. However, the Aspect feels pretty great as well, is slightly more abrasion-resistant, and will save you some cash. For more, read our review of the Aspect Midweight.

Smartwool Classic All-Season ($100)
Pulling sleeve down on Smartwool Classic All-Season Base Layer
4.3/5

The Classic All-Season is a lightweight merino base layer that offers soft next-to-skin comfort and enough warmth for shoulder seasons or low-to-moderate winter activity. It’s not the best choice for high-output pursuits or deep-winter cold, and its thin fabric sacrifices some longevity.

Fabric(s)
88% merino, 12% nylon
Fabric weight
150 g/m²
Weight
6 oz.
Variations
Crew, quarter-zip
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Warmth

3/5
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Breathability

3/5
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Durability

2.5/5
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Comfort

4.5/5
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Odor Resistance

4.5/5
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Sustainability

3.1/5
Smartwool Classic Thermal Merino 1/4 Zip ($130)
Smartwool Classic Thermal Merino Base Layer material comparison
4.6/5

Smartwool's Classic Thermal is an exceptionally warm, 100% merino base layer for winter conditions. It's soft, cozy, and odor resistant. Given its heavyweight construction, it can quickly become too warm; because of this, we only recommend it for low-output activities in cold weather.

Fabric(s)
100% merino wool
Fabric weight
250 g/m²
Weight
10.5 oz.
Variations
Crew, quarter-zip, hoodie
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Warmth

4.5/5
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Breathability

2/5
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Durability

2.5/5
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Comfort

5/5
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Odor Resistance

5/5
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Sustainability

3.7/5
Ridge Merino Aspect ($80)
Layering over Ridge Merino Aspect Midweight Merino Wool Base Layer LS
4.7/5

The Aspect is a high-quality merino base layer that’s more affordable than much of the competition. Well-designed thumb loops and a drop hem contribute to a classy vibe, and the addition of nylon helps with durability, structure, and dry time. However, inventory can be spotty.

Fabric(s)
84% merino, 16% nylon
Fabric weight
180 g/m²
Weight
8.3 oz.
Variations
Quarter zip, turtleneck (w), hoody (m)
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Warmth

3.5/5
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Breathability

3/5
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Durability

3.5/5
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Comfort

4.5/5
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Odor Resistance

4.5/5
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Sustainability

2/5

Is the Classic All-Season for You?

If you want a fairly lightweight, comfortable merino base layer for hiking, running, travel, and moderate cold-weather wear, the Smartwool Classic All-Season is a solid choice. It plays best during shoulder season and medium activity levels rather than high-output pursuits, whether during winter or otherwise. But if soft on-skin feel, odor resistance, and stretchy comfort matter more to you than longevity or sweat management (neither of which it’s great at), the All-Season should keep you happy across a wide range of activities and conditions.

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