Smartwool · Lightweight merino quarter-zip · Mid-range
Smartwool Classic All-Season Merino Base Layer 1/4 Zip
Best overallCold-weather running guide
The most consistently recommended merino base layer for winter running right now: thin enough to wear alone when it's merely chilly and easy to vent through the zip, but it needs a shell or midlayer once it gets truly cold.
- List price
- $105Men's list price on smartwool.com; the page also shows a $57-$105 range across variants, so some colors may be discounted. Women's price not checked. The crew version is $100 per Treeline.
- Fits
- Men's, Women's
- Warmth
- Light
- Wind
- None
- Water
- None
- Visibility
- None
- Temperature range
- 35 to 55°F (2 to 13°C) Our estimate from the construction
- Best for
- Runners who want one odor-resistant merino top that works alone in mild cold and as a base layer under a jacket in winter.
- Not for
- Anyone who needs standalone warmth below freezing or a rugged top that shrugs off abrasion.
Downsides
- Little warmth on its own in real cold
- OutdoorGearLab raised durability concerns about the thin fabric
- Treeline found it less technical than some vented or hybrid rivals
Specs
| Materials | 88% merino wool, 12% recycled nylon |
|---|---|
| Fabric weight | 150 g/m² |
| Fit | Slim |
| Neck | 1/4-zip, 8 in zipper (men's M) |
| Thumbholes | No |
| Odor control | Merino; brand lists odor resistance |
| Style number | SW002819 |
Features
- 150 g/m² merino-nylon jersey
- Quarter-zip with 8 in center-front zipper (men's M)
- Slim, close-to-body fit
- Odor-resistant merino
- Same fabric also sold as a crew
What reviewers say
Named the Classic All-Season 1/4 Zip ($105) its best base layer shirt for winter running, citing versatility on its own in mild cold or under a jacket, plus the zip and high collar for managing heat.
iRunFar: Best Cold Weather Running Gear of 2026 · Oct 21, 2026
Rated the Classic All Season (crew tested, quarter-zip also offered) Best Overall at $100, praising durability, versatility, sizing and odor resistance through ultras and high-output trail runs; noted it is less technical than some competitors.
Treeline Review: Best Base Layers of 2026 (Long-Term Tested) · Feb 21, 2026
Gave the women's Classic All-Season crew a Best Buy and called the line a good fit for runners training through cold months; downsides were durability and limited standalone warmth.
OutdoorGearLab: Best Base Layer (GearLab men's guide) · Apr 1, 2026
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