{
 "id": "smartwool-classic-thermal-merino-1-4-zip",
 "name": "Smartwool Classic Thermal Merino Base Layer 1/4 Zip",
 "brand": {
  "name": "Smartwool",
  "url": "https://agenticrecs.com/brands/smartwool/"
 },
 "model": "Classic Thermal Merino Base Layer 1/4 Zip",
 "department": {
  "id": "running",
  "name": "Running",
  "url": "https://agenticrecs.com/running/"
 },
 "category": {
  "id": "running-base-layers",
  "name": "Running base layers & tops",
  "url": "https://agenticrecs.com/running/base-layers/",
  "json_url": "https://agenticrecs.com/running/base-layers/index.json",
  "schema": "running-apparel"
 },
 "subtype": "midweight merino quarter-zip",
 "msrp_usd": 130,
 "msrp_note": "Men's list price on smartwool.com; the page also shows a $72-$130 range across variants. Treeline lists the crew version at $125.",
 "price_tier": "Mid-range",
 "price_checked": "2026-10-26",
 "attributes": {
  "fits": [
   "men"
  ],
  "warmth": "mid",
  "wind": "none",
  "water": "none",
  "visibility": "none",
  "temp_range_f": [
   20,
   40
  ],
  "temp_range_c": [
   -7,
   4
  ],
  "temp_basis": "estimate"
 },
 "awards": [
  {
   "label": "Warmest",
   "guide": "cold-weather-running",
   "chapter": "base-layers",
   "url": "https://agenticrecs.com/guides/cold-weather-running/base-layers/"
  }
 ],
 "summary": "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.",
 "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"
 ],
 "where_to_buy": [
  {
   "retailer": "Smartwool",
   "url": "https://www.smartwool.com/en-us/products/mens-classic-thermal-merino-base-layer-1-4-zip-sw002821",
   "affiliate": false
  }
 ],
 "materials": "100% merino wool",
 "style_number": "SW002821",
 "key_features": [
  "250 g/m² 100% merino",
  "Quarter-zip with 10 in center-front zipper (men's M)",
  "Slim fit",
  "Odor-resistant merino"
 ],
 "specs": {
  "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"
 },
 "official_url": "https://www.smartwool.com/en-us/products/mens-classic-thermal-merino-base-layer-1-4-zip-sw002821",
 "sources": [
  {
   "publisher": "OutdoorGearLab",
   "title": "Best Base Layer (GearLab men's guide)",
   "url": "https://www.outdoorgearlab.com/topics/clothing-mens/best-base-layer",
   "date": "2026-04-01",
   "finding": "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."
  },
  {
   "publisher": "Treeline Review",
   "title": "Best Base Layers of 2026 (Long-Term Tested)",
   "url": "https://www.treelinereview.com/gearreviews/best-base-layers",
   "date": "2026-02-21",
   "finding": "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."
  }
 ],
 "evidence": {
  "specs_from": "https://www.smartwool.com/en-us/products/mens-classic-thermal-merino-base-layer-1-4-zip-sw002821",
  "reviews_summarized": 2,
  "tested_by_site": false
 },
 "guides": [
  {
   "guide": "cold-weather-running",
   "chapter": "base-layers",
   "url": "https://agenticrecs.com/guides/cold-weather-running/base-layers/"
  }
 ],
 "last_verified": "2026-10-26",
 "url": "https://agenticrecs.com/products/smartwool-classic-thermal-merino-1-4-zip/",
 "markdown_url": "https://agenticrecs.com/products/smartwool-classic-thermal-merino-1-4-zip/index.md",
 "json_url": "https://agenticrecs.com/products/smartwool-classic-thermal-merino-1-4-zip/index.json"
}