Smartwool · Midweight merino quarter-zip · Mid-range
Smartwool Classic Thermal Merino Base Layer 1/4 Zip
WarmestCold-weather running guide
The warmer sibling of the All-Season: a 250 g/m² all-merino quarter-zip that reviewers rank among the best base layers for serious cold, though it costs more and needs gentler care than synthetics.
- List price
- $130Men's list price on smartwool.com; the page also shows a $72-$130 range across variants. Treeline lists the crew version at $125.
- Fits
- Men's
- Warmth
- Midweight
- Wind
- None
- Water
- None
- Visibility
- None
- Temperature range
- 20 to 40°F (−7 to 4°C) Our estimate from the construction
- Best for
- Easy or long runs well below freezing, and runners who run cold and want merino warmth under a shell.
- Not for
- Hard efforts in mild weather, where heavier wool runs hot, or anyone wanting a tough, low-maintenance top.
Downsides
- Delicate wool that needs careful washing
- Expensive
- Treeline sees it as a cold-weather layer more than a running piece
Specs
| Materials | 100% merino wool |
|---|---|
| Fabric weight | 250 g/m² |
| Fit | Slim |
| Neck | 1/4-zip, 10 in zipper (men's M) |
| Thumbholes | None listed |
| Odor control | Merino; brand lists odor resistance |
| Style number | SW002821 |
Features
- 250 g/m² 100% merino
- Quarter-zip with 10 in center-front zipper (men's M)
- Slim fit
- Odor-resistant merino
What reviewers say
Editors' Choice for the men's Classic Thermal 1/4 Zip ($130), citing warmth for its weight, a soft feel, a venting zip and breathability even when damp; downsides were delicate wool, price and care needs.
OutdoorGearLab: Best Base Layer (GearLab men's guide) · Apr 1, 2026
Named the Classic Thermal (crew, $125, 250 gsm, 100% merino) best for extreme cold, praising warmth, durability and sizing, while positioning it for general cold-weather use rather than running.
Treeline Review: Best Base Layers of 2026 (Long-Term Tested) · Feb 21, 2026
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