Best merino wool base layer brands
Merino wool is the best natural fiber for a base layer. It regulates temperature in both directions — trapping warmth when you are cold and releasing excess heat when you warm up — without the synthetic feel or odor buildup of polyester. The fiber is naturally non-itchy at fine micron counts (18.5 microns or under), wicks moisture away from skin, and resists bacterial growth so you can wear it across multiple days without washing.
When choosing a merino base layer, the key specifications are: GSM weight (150 gsm for lightweight/all-season, 200 gsm for midweight/winter, 250 gsm+ for heavyweight/cold conditions), merino percentage (80%+ for genuine wool performance), and certification (ZQ or RWS confirms mulesing-free sourcing). The brands below make merino wool activewear and base layers and are listed in The Plain Thread directory.
Outdoor basics and activewear in merino wool and organic cotton for men and women.
UK surf and outdoor brand making apparel in organic cotton, hemp, and merino.
New Zealand merino wool outdoor base layers and apparel for men, women, and kids.
Norwegian women's activewear brand making merino wool base layers and technical clothing for outdoor sports.
Merino wool outdoor apparel for men and women with a Himalayan-inspired aesthetic.
100% New Zealand merino wool base layers and travel clothing for men and women.
New Zealand ZQ merino wool ski and outdoor apparel for men and women.
Outdoor brand making apparel in organic cotton, hemp, and merino wool with strong environmental advocacy.
Merino wool socks, base layers, and outdoor apparel for men, women, and kids.
Japanese outdoor brand making merino wool and natural material apparel for men and women.
Merino wool activewear and base layers for men and women at mid-market prices.
Common questions about merino base layers
What gsm merino is best for a base layer?
GSM (grams per square meter) determines the weight and warmth of a merino base layer. For a general-purpose base layer suited to most activities and seasons, 150-200 gsm is the most useful range. At 150 gsm you get a lightweight layer that works in spring and fall and as a warm-weather base in cold environments. At 200 gsm the fabric has more substance — better for winter activities, ski touring, or when you expect sustained cold. Above 250 gsm is midlayer territory, better as a second layer than a base. Most base layer ranges offer at least two weights; buying both covers most conditions.
Is merino wool better than synthetic base layers?
For most people and most conditions, yes. Merino regulates temperature in both directions: it traps warmth when you are cold and releases heat when you warm up. Synthetic base layers can only insulate; they do not cool. Merino also resists odor far better than any synthetic — the natural structure of wool fiber inhibits bacterial growth, so you can wear a merino base layer for multiple days without the smell that accumulates in a polyester layer overnight. Merino is also more comfortable at skin contact in most conditions, especially when wet. The tradeoff is durability: merino is more delicate than nylon or polyester and requires careful washing.
Can you wear merino wool base layers in summer?
Yes. Lightweight merino (150 gsm) is an excellent summer base layer in specific contexts: hiking in variable mountain weather, activities that generate heat followed by wind exposure, or anywhere you want odor resistance across a multi-day trip without laundry access. Merino does not overheat you the way a heavier synthetic layer might — the fiber actively moderates temperature rather than just trapping it. In genuinely hot, humid conditions (tropical travel, summer urban heat), linen or very lightweight cotton performs better; but for active outdoor use in temperate summer conditions, light merino is a reasonable choice.
How do you wash a merino base layer?
Machine wash on a wool or delicate cycle in cool water (30°C maximum). Use a detergent designed for wool — standard detergents strip lanolin from the fiber and degrade it over time. Do not use fabric softener. Do not tumble dry — the heat and agitation of a dryer causes felting and irreversible shrinkage. Instead, reshape the garment while damp and lay flat to air dry. Never wring merino; gently press water out by rolling it in a towel. Following these steps, a quality merino base layer holds up through hundreds of wash cycles without significant degradation.
What certifications should a merino base layer have?
Two certifications are most relevant. ZQ Merino is the more comprehensive: it covers animal welfare (mulesing-free), land management, and social responsibility for the farms and is issued by The New Zealand Merino Company. Responsible Wool Standard (RWS) is a Textile Exchange standard covering humane treatment and sustainable land management, traceable through the supply chain. Both are meaningful signals that the wool is mulesing-free and responsibly sourced. OEKO-TEX Standard 100 certifies that the finished product contains no harmful chemicals at detectable levels — relevant for a garment worn next to skin. The strongest base layers will carry at least one of ZQ, RWS, or OEKO-TEX.