A midweight, 100% merino wool long-sleeve base layer with a slim fit and flatlock seams. People pick it for warmth on cold mornings and because it can be worn for days without smelling.
Specs
- Fabric: 100% merino wool (ZQ certified), 250 g/m² midweight interlock knit
- Fit: slim
- Construction: flatlock seams, offset shoulder and side seams
- Sizes: men's XS–3XL; women's version sold separately
- Guarantee: Smartwool guarantee within two years of purchase
- Made in Vietnam
- Price: $125 (Smartwool and REI, Oct 2026)
What reviewers say
Owners and reviewers agree on comfort, warmth without bulk, sweat handling and odor resistance. Backdrop Journal's reviewer wore it for a month in alpine conditions down to about -12°C and had no complaints beyond it feeling a bit heavier than synthetics. REI shoppers rate it 4.8 of 5 over 1,100 reviews, but durability is the steady complaint: many report small holes after a few months of wear or washing, and some feel newer versions are not as tough as older ones. That's the main thing to weigh against the price.
Good
- Warm for its weight
- Soft, no itch for most people
- Strong odor resistance; can be worn several days
- Seams placed to avoid pack-strap chafe
Not so good
- Expensive
- Many owners report holes developing within months
- Slower to dry and a bit heavier than synthetic base layers
Who it's for
Hunters, campers and winter hikers who want a warm next-to-skin layer for cold mornings and multi-day trips. If you are hard on clothes or want something that lasts for years, a merino-synthetic blend may hold up better.
Sources
Last checked 2026-10-19. Specs from the maker; review notes summarized in our own words.