Smartwool Classic All-Season Merino Long Sleeve

We field-tested the Smartwool Classic All-Season Merino Long Sleeve across multiple seasons, layering systems, and conditions from high-output ridge ascents to static belays in sub-freezing wind. This review reflects months of real wear, washing, and abuse.

How it performed

Merino's reputation rests on four pillars: warmth for weight, breathability, odor resistance, and next-to-skin comfort. We score each independently so you can weight them for your own use case.

Warmth and breathability

In testing, the fabric weight maps closely to real-world warmth, but knit structure matters just as much. We logged comfort ranges across activity levels and ambient temperatures to land our warmth score.

Comfort and fit

Next-to-skin feel, flatlock seams, and cuff construction all factor into our comfort rating. We note where the cut runs athletic versus relaxed so you can size correctly.

Durability and odor resistance

We tracked pilling, seam integrity, and odor build-up over repeated multi-day wear without washing. Merino's natural odor resistance is its quiet superpower, and we report how this garment holds up.

Bottom line

See our verdict and scores above for the quick take. For most readers, the right base layer comes down to matching fabric weight to your climate and activity and this review is built to help you do exactly that.