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Arc’teryx Rho Merino Crew Neck LS Base Layer Review

Eli Bernstein bio photo
ByMultiple Authors
Mar 24, 2026
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Our Take:
4.6/5

The Arc’teryx Rho Merino Crew Neck LS ($120) is a warm, exceptionally comfortable merino base layer that performs best in cold conditions and at moderate output. With its plush feel, chill-stopping warmth, and high odor resistance, it’s one of the best winter-weight base layers we’ve tested. It balances insulation and breathability well, and though the fit might run a bit relaxed for some, it’s a standout for versatile cold-weather layering.

Warmth

Warmth

4.5/5
Breathability

Breathability

2.5/5
Durability

Durability

3.5/5
Comfort

Comfort

5/5
Odor Resistance

Odor Resistance

5/5
Sustainability

Sustainability

3.5/5

Fabric(s)

95% merino wool, 5% elastane + nylon

Fabric weight

240 g/m²

Weight

10.2 oz.

Variations

Crew, zip-neck

Pros

Luxuriously soft, comfortable fabric thanks to high merino content.
Excellent warmth and moisture-wicking, which feels great in cold conditions.
Outstanding odor resistance, even after repeated use.

Cons

Sleeves run a bit long, especially if you prefer a trim fit.
On the expensive side (although merino build and overall quality are worth it).

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

The Arc’teryx Rho Merino Crew Neck LS has become my go-to base layer when the temperature drops. I’ve worn it consistently over the past five months for shoulder-season trail running, winter hiking, and resort skiing, and it shines in cold conditions. The Rho Merino worked well as a standalone layer for trail runs with temperatures in the high 40s and low 50s, and it’s equally at home as a ski base layer under a midlayer and a shell when things get really cold—down into the 20s and below.


I used it extensively in the Alps in late fall, including hiking in snowy conditions around Chamonix (layered under a Black Diamond Access Down Hoody), and early-season ski laps on the Zermatt glacier with a wool midlayer on top. Compared to synthetic base layers like the Patagonia Capilene Thermal Weight, the Rho feels noticeably warmer and cozier. In terms of merino competitors, it’s slightly less warm than the Smartwool Classic Thermal (250 g/m²), but it offers better insulation than lighter options such as the Ortovox Rock’N’Wool (185 g/m²) or the Smartwool All-Season (150 g/m²). For use across late fall and all of winter, it’s right in the sweet spot.

Despite its warmth, the Rho Merino manages moisture impressively well. I’ve sweated heavily in this layer while trail running, resort skiing, and hiking, and it consistently wicked moisture away from my skin without ever feeling clammy. That said, it’s not the base layer I’d choose for high-output ski touring or shoulder-season efforts; it’s simply too warm, and—unlike synthetic materials—merino doesn’t dry quickly once wet. All told, the Rho Merino is a cold-weather, moderate-output specialist.


If you use the Rho in the right conditions, though, it rewards your selection. One standout moment came during a vertical kilometer run in Chamonix. I was pushing hard uphill and sweating heavily, then transitioned into much colder, snowy, and windy conditions at the summit. After throwing on a wind shell, I stayed warm on the descent despite how much I’d sweated on the way up. That kind of stay-warm moisture management is where this layer really excels.

After roughly five months and 40 days of use, the Rho Merino is holding up exceptionally well. Its main fabric makeup is 95% merino wool and 5% elastane. Merino is not a particularly durable fiber, but Arc’teryx reinforces it with a nylon core, which gives it a noticeable durability advantage over 100% merino base layers like the Ortovox Rock’N’Wool or the Smartwool Classic All-Season. There are no signs of thinning, pilling, or seam issues so far.


One notable incident I experienced involved running directly into a metal signpost during a trail run in Chamonix. My wind shell tore, but the Rho underneath was completely unharmed. This feels like a piece that will last for many seasons with proper care, though I’ll certainly try to avoid metal signs in the future.

The Arc’teryx Rho Merino is the most comfortable base layer I’ve ever worn. The fabric is plush, soft, and stretchy, with none of the scratchiness sometimes associated with merino. The material’s 5% elastane adds just enough stretch to allow unrestricted movement without the fit feeling loose or sloppy. I’ve worn it for long runs, full days in the mountains, and plenty of casual time at home, and it never becomes irritating. It simply disappears once it’s on.


I found the fit of the Rho Merino more relaxed than a traditional skin-tight base layer, closer to a well-loved long-sleeve T-shirt than a compression shirt. Personally, I love this feel—it’s far more comfortable than the tight, athletic cuts of many technical base layers, like The North Face’s Summit Series Pro 120 or the Smartwool Intraknit Thermal. I suspect sizing down would yield a more performance-oriented fit, but as tested, the comfort is unmatched.

This is where the Rho Merino (and, to be fair, other majority merino base layers) truly separates itself from synthetic competitors. This base layer’s odor retention is virtually nonexistent. I’ve worn it for multiple runs, hikes, and travel days without washing, and it never developed that persistent stink that’s basically unavoidable with synthetics.


For ski trips, travel, or multi-day outings where laundry isn’t an option, this is a huge advantage. Compared to synthetic base layers that seem to smell permanently after a few uses, no matter how well you wash them, the Rho Merino is a revelation—and it’s made me a full convert to wool for traveling and cold-weather layering.

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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: 6’2”, 175 lb.; 41" chest, 31" waist
Size tested: Men’s large


I typically wear a men’s large, and the Arc’teryx Rho Merino in that size fits like a standard, non-technical long-sleeve T-shirt. The sleeves run slightly long, which initially made me consider sizing down, but the shoulder width, chest, and torso length were spot-on, so I stuck with the large. In practice, the sleeve length wasn’t an issue.


If you prefer a tighter, more technical base-layer fit, consider sizing down. All in all, the Rho has a relaxed, comfortable cut that prioritizes wearability and movement over compression. And no matter whether or not you size up, it should slide effortlessly beneath whatever layers you throw on top.

Smartwool Classic Thermal Merino ($125): $5 More Warmth
The 250-gram, 100% merino Classic Thermal Merino is about as heavy as base layers get—slightly beefier than the Rho’s 240 g/m²—and can comfortably take you into the teens (and likely lower) as part of a winter layering system. The tradeoff is versatility: the Classic Thermal can feel like overkill for anything but the coldest days, limiting its range across different activities. And while it’s exceptionally soft—arguably even cozier than the Rho—it lacks a nylon core, making it less durable over time. If you’re mostly skiing cold resort days, the Classic is a great pick; for broader use, the Rho is the more well-rounded option. For more, read our review of the Smartwool Thermal Merino

Arc’teryx Rho LT Crew ($100): Better for High-Output
Instead of merino, the Rho LT uses a polyester-elastane blend (85% polyester, 16% elastane), making it slightly less warm but noticeably more breathable. That difference is especially apparent during high-output efforts like ski touring, where the Rho LT feels far more comfortable and dries much faster if you start to sweat. Despite the shift to synthetics, it doesn’t give up much in the way of comfort—the fleece interior is soft against the skin and holds its own against the cozier feel of the merino version. The tradeoff, of course, is odor resistance: while the Rho LT performs reasonably well for a synthetic, it can’t match the natural anti-odor properties of merino. But unless you’re prioritizing maximum warmth or simply prefer the feel of wool, the Rho LT stands out as the more versatile—and better value—option. For a deeper dive, read our Rho LT review.

Arc’teryx Rho Merino Crew Neck LS ($120)
Hiking above hut in the Arc'teryx Rho Merino Wool Crew Neck LS base layer
4.6/5

The Rho Merino is a warm, exceptionally comfortable base layer that excels in cold conditions and moderate-output use. With its plush feel, strong odor resistance, and relatively durable build (compared to 100% merino base layers), it’s one of the top winter-weight options.

Fabric(s)
95% merino wool, 5% elastane + nylon
Fabric weight
240 g/m²
Weight
10.2 oz.
Variations
Crew, zip-neck
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Warmth

4.5/5
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Breathability

2.5/5
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Durability

3.5/5
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Comfort

5/5
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Odor Resistance

5/5
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Sustainability

3.5/5
Smartwool Classic Thermal Merino Base Layer Crew ($115)
Smartwool Classic Thermal Base Layer fit under ski jacket
4.6/5

The Classic Thermal is an exceptionally warm, 100% merino base layer tailor-made for deep winter conditions. It's soft, cozy, and odor resistant, although you’ll have to treat it with care if you want it to last.

Arc'teryx Rho LT Crew Neck ($100)
Arc'teryx Rho Crew Neck base layer getting ready for skiing (2)
4.6/5

A smooth exterior, brushed fleece interior, and highly stretchy design make the Rho LT more comfortable than most synthetic base layers. It also excels in wicking moisture away from the skin and dries quickly. However, the cozy fleece is hot in mild conditions.

Fabric(s)
84% polyester, 16% elastane
Fabric weight
190 g/m²
Weight
7.9 oz.
Variations
Zip neck, hoody
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Warmth

4/5
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Breathability

4/5
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Durability

4/5
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Comfort

5/5
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Odor Resistance

4/5
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Sustainability

3.3/5

Is the Rho Merino for You?

The Arc’teryx Rho Merino Crew Neck LS is one of the highest-performing merino base layers we’ve tested. It stands out for its impressive warmth and next-to-skin comfort, and the merino-wrapped nylon core adds a welcome boost in durability over more traditional wool designs. It’s not the best fit for high-output use in mild conditions, but as a foundational layer for cold-weather pursuits—like winter hiking, skiing, and trail running—it’s a dialed, dependable option.

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