Smartwool Men's Classic All-Season Merino Base Layer Long Sleeve review: pricey but worth it

A luxuriously comfortable year-round-useful merino base layer

A man wearing a Smartwool Men's Classic All-Season Merino Base Layer Long Sleeve sitting on a stony beach.
(Image: © Pat Kinsella)

Advnture Verdict

Overall this is an excellent, very versatile and extremely comfortable long-sleeved base-layer top, with an intelligent design and seams that make it particularly comfortable when worn with a backpack. Made almost entirely with merino and with good consideration for the environment, it feels and looks great, is available in a bold spectrum of colors, and works well for an exhaustively wide range of outdoor activities throughout the year.


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    Wicks moisture brilliantly

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    Highly breathable

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    Great odor control

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    Very comfortable

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    Excellent temperature control


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    Takes time to dry

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    No thumb hoops

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    Sizes quite large

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Meet the reviewer

best fleece jackets: Artilect Halfmoon Bio Pullover
Pat Kinsella

Pat has hiked all over the world, his adventures taking him to Mont Blanc, the roof of Western Europe; the Norwegian Alps; the highest peaks on Australia; and New Zealand’s Great Walks – among others. He’s an experienced tester of hiking footwear and gives each pair a thorough thrashing before reviewing.

Smartwool Men's Classic All-Season Merino Base Layer Long Sleeve: first impressions

It’s always nice putting on a new merino garment – the slight initial chill of the material in the morning soon gives way to a protective feel, and the fabric is, in my opinion, unrivalled in its next-to-skin comfort. Nothing else comes anywhere near it. So, suffice to say, I was excited to start testing out the Men's Classic All-Season Merino Base Layer Long Sleeve from Colorado-based merino specialist Smartwool, which is close to 90% merino wool. 

The remainder of the material mix is made up from recycled nylon, which adds strength to the fabric – one of the few weaknesses of merino garments is a tendency to develop holes after a bit of wear and tear, and the addition of a tough synthetic like nylon should help stop this happening, improving the useful life of the top. The fact that it’s recycled nylon is positive, and it’s also worth noting that the merino wool used here has been certified as responsibly sourced, and plant-based eco-friendly dyes have been used to create the selection of funky color options.


• List price: $90 (US) / £85 (UK)
• Materials: Merino wool (88%) and recycled nylon (12%)
• Sizes: S–XXL
• Weight: 166g / 5.9oz
• Colors: Black / Fox brown / Iron heather / Pewter blue wash / Fern green / Laguna blue-deep navy
• Compatibility: Walking, hiking, biking, trekking, backpacking, mountaineering, trail running, snow sports and camping 

With such a high level of wool content, the attributes of this top will be familiar to merino fans: aside from offering luxurious comfort levels (enhanced here by the flatlock seams), it promises to let your body breathe really well during outdoor activities, to wick moisture away when you sweat, to fight off any accumulation of bad odors with its naturally occurring bacteria-busting enzymes and, perhaps most importantly, to help you regulate your temperature across all four seasons.

All these benefits of merino-based garments are well known, so I had high expectations of this top when I started trail testing it to see how it compares with the best base layers on the market.

Smartwool Men's Classic All-Season Merino Base Layer Long Sleeve: design and construction

A close-up of the neckline on a Smartwool Men's Classic All-Season Merino Base Layer Long Sleeve.

Lightweight with a generous fit, the merino blend of the Smartwool Men's Classic All-Season Merino Base Layer Long Sleeve makes for a cozy, breathable tee. (Image credit: Pat Kinsella)

Somewhat strangely, I can’t see the GSM (grams per square meter, which indicates how thick the fabric is) of this garment anywhere on the Smartwool website or the packaging, but it is noticeably thin. This plays into the all-season style, and merino does have the remarkable ability to help you stay warm when it’s cold outside, and cool when conditions are hot. The thickness of the material of course comes into this, and you will need to combine this particular top with a good mid layer in the form of a decent fleece or puffer jacket in order to remain comfortable in the midst of winter, or at altitude. And while merino is wonderful for all sorts of reasons I have already detailed, it does take some time to dry if you do get it wet, so a reliable waterproof jacket might be required as an outer layer.

In the shoulder seasons of spring and fall, and all through summer, however, this lightweight construction will help you stay shielded from the sun and wind when required, and then provide adequate thermal protection during chilly mornings and evenings at the crag or in camp.

Smartwool describe this garment as having a slim fit. There is no elastane or Lycra content in the fabric, so it doesn’t feel tight or supply any compression, but the thin, lightweight material does hug your contours. On test I actually found the sizing to be quite generous, and the large top I’ve been wearing (my usual size selection) was a tad baggier than I typically like base layers to be – so bear this in mind if you often fall between sizes. 

Smartwool Men's Classic All-Season Merino Base Layer Long Sleeve: on the trails

A man wearing a Smartwool Men's Classic All-Season Merino Base Layer Long Sleeve walks along a woody trail.

The Smartwool Men's Classic All-Season Merino Base Layer Long Sleeve is ideal for almost all outdoor activities. (Image credit: Pat Kinsella)

I've been wearing the Smartwool Men's Classic All-Season Merino Base Layer for several weeks, as winter has segued into spring in England’s soggy south west, while doing dynamic activities ranging from hiking and trail running to cycling and climbing. 

As expected, it feels super soft and smooth next to my skin, and I have experienced zero itchiness or scratchiness. The comfort levels are further improved by the flatlock seams, but one of the features I particularly like about this top is the offset shoulder and side seams, which Smartwool has employed to reduce the risk of rubbing and chafing when you’re wearing it while hauling a hiking backpack, daypack or hydration pack. This is a great touch.

A close-up of the shoulder of a man wearing a Smartwool Men's Classic All-Season Merino Base Layer Long Sleeve.

Offset shoulder seams mean the Smartwool Men's Classic All-Season Merino Base Layer Long Sleeve doesn't chafe when worn with a backpack. (Image credit: Pat Kinsella)

One niggle I do have with this top is that it lacks thumb loops, so the sleeves ride up when you put on a fleece or jacket, and it’s harder to avoid ending up with some exposed skin if you’re wearing it with gloves while hiking, biking, running or skiing. Thumb hooks or loops are such a simple and useful addition to base and midlayers, and I really don’t understand why more brands don’t use them. There is a hang loop on the back of the collar of this top, which can be handy (but it’s definitely not as necessary as thumb loops).

Pat Kinsella

Author of Caving, Canyoning, Coasteering…, a recently released book about all kinds of outdoor adventures around Britain, Pat has spent 20 years pursuing stories involving boots, bikes, boats, beers and bruises. En route he’s canoed Canada’s Yukon River, climbed Mont Blanc and Kilimanjaro, skied and mountain biked through the Norwegian Alps, run an ultra across the roof of Mauritius, and set short-lived records for trail-running Australia’s highest peaks and New Zealand’s Great Walks. He’s authored walking guides to Devon and Dorset, and once wrote a whole book about Toilets for Lonely Planet. Follow Pat’s escapades on Strava here and Instagram here.