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The best merino wool base layers

A good merino base layer might be an investment, but it's certainly worth it for its temperature-regulating, moisture-wicking properties that keep you comfortably warm and dry. Whether you're an extreme sports enthusiast or a city dweller, the best merino wool base layers come in weights between 165 and 300 grams per square meter (GSM), providing a layer of warmth without the bulk. The right one for you will come down to the weather you're dressing for and your budget.

While there doesn't seem to be a universally accepted guide to GSM (what is lightweight to some might be deemed mid-weight to others), a merino wool base layer around the 170 GSM range generally makes a good lightweight base layer for relatively mild days. A mid-weight base layer between 200 and 300 GSM will see you through colder temperatures, and heavyweight layers, which typically go from 300 GSM and up, are most appropriate for days with the deepest chill. You might also see the number of microns listed for merino wool garments, which indicates how fine the fibers are — a lower number yields a softer fabric, and around 17.5 to 18.5 microns is considered ideal.

A good merino wool T-shirt can serve as an all-purpose base layer, and it's an excellent way to test the merino wool waters if you’re just starting out since they're the most budget-friendly. They can be worn on their own in good weather but are also easy to layer if the temperatures fluctuate. Meanwhile, a wool quarter-zip or hoodie can serve as outerwear but will still fit under a coat if it's especially cold out. For activities like skiing, snowboarding, or hiking in colder weather, you may want to spring for a base layer on your bottom half as well.

From an ultra-fine tee to a heavy-duty hoodie, these merino wool base layers offer warmth without weighing you down, all while delivering big on softness.

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1. The mid-weight pullover

Men's:

This 18.5-micron merino wool pullover is hardy enough for the great outdoors but also looks nice enough to transition to a night out on the town. The mid-weight Meriwool base layer is made with 250 GSM merino wool in a soft, itch-free construction. It’s backed by a one-year limited warranty. While it's technically washer and dryer safe, the manufacturer recommends hand washing and air drying for best results. "Fit and finish, strength of seams, durability of fabric, quick dry capability, machine wash- and dryer-friendliness, resistance to odors, etc. - it's all up to snuff," one Amazon reviewer wrote.

  • Available colors: 9
  • Available sizes: Small — XX-Large

Women's:

This 100% merino mid-weight crewneck base layer from Minus33 comes in a 230 GSM, 18.5-micron knit. Boasting flatlock seams and a tagless design for all-day comfort, it even features UPF 50+ for those seeking sun protection. The princess seams provide a tailored look on this versatile, machine-washable top.

"These shirts are phenomenal," one reviewer noted. "Excellent material, looks and fits great, high quality, perfect weight. I bought two, size 2X, and the matching bottom, and wore them for 8 days in Iceland as a base layer, generally directly under a vest or rain coat. They are the definition of high performance."

Looking for more options? This budget-friendly merino wool base layer has a similar weight with less sticker shock, and this is another highly rated shirt that has earned REI's backing.

  • Available colors: 11
  • Available sizes: X-Small — 3X-Large

2. The lightweight tee

Men's:

This solid merino wool T-shirt is a versatile base layer that is soft, light, and feels like an undershirt, according to reviewers, yet it's still plenty warm. It's made from organic, New Zealand-sourced wool with a 165 GSM weight and superfine 17.5 micron fibers.

"I had never owned a wool tee shirt prior to purchasing this one [...] but I am absolutely sold," one reviewer noted, adding, "I do a lot of hiking and I sweat profusely. The wool tee kept me cool and odor free and far more comfortable than cotton." You can toss this shirt in the washing machine, and the brand even includes a pair of socks for free.

  • Available colors: 20
  • Available sizes: Small — XX-Large

Women's:

It's not surprising that the makers of the best merino wool tee for men also happen to offer an excellent merino wool T-shirt for women, too. They share the same 165 GSM, 17.5-micron organic merino wool, but this version has a fitted V-neck and more contoured cut through the body. "This 100% wool short sleeved shirt is a perfect weight and is perfect as an undershirt in cooler weather," one fan noted. "It is better than a cotton T-shirt in hot weather. The weave is perfect for dissipating heat and it feels great against the skin."

  • Available colors: 6
  • Available sizes: Small — X-Large

3. The heavyweight hoodie

Men's:

Admittedly, this 400 GSM, 18.5 merino wool zipped hoodie comes with a hefty price tag, but it's an ultra-warm option that will have you feeling completely insulated when the weather calls for it. Plus, there are thoughtful design details that make this machine-washable option one you'll reach for when you need a reliable layer, including thumb holes, a cozy brushed interior, and a drawstring hood. For a more budget-friendly hooded option, you might also consider this henley hoodie.

  • Available colors: 2
  • Available sizes: Small — XX-Large

Women's:

This heavyweight merino wool hoodie is woven from 320 GSM, 18.5 micron wool that will help you stay warm in extreme cold. It has a stand collar that keeps out drafts and a hood for extra coziness, with a full-length front zip opening. It has a streamlined cut through the body, and everything is detailed with piping at the seams for a finished look. Two zippered pockets offer plenty of room for your keys and your hands.

  • Available colors: 2
  • Available sizes: X-Small — X-Large

4. The bottoms

Men's:

These Minus33 merino wool base layer bottoms have over 1,000 reviews on Amazon, many of which note it for being especially soft, warm, comfortable, and high quality. These machine-washable bottoms are made from a hefty 230 GSM interlock knit woven with ribbed ankle cuffs and a fly to keep out drafts. They come in sizes up to 6X-large, as well as in tall inseams.

"Holy hell – These are FANTASTIC," one reviewer remarked. "I wore them for the entire week and could barely tell that they were there. Very warm, comfortable, breathable, look tight but don't feel tight (probably the best feature in my opinion), crotch fit perfectly, and the bottom cuffs are a great addition."

  • Available colors: 10
  • Available sizes: X-Small – 6X-Large

Women's:

These 208 GSM merino wool base layer bottoms come from the popular Smartwool 250 series. The line has earned rave reviews as a base layer to wear across seasons. Petite Amazon reviewers noted some extra length at the ankles, but tall shoppers will likely appreciate the added length. "Very soft and VERY warm! I wore it on days when I was hiking in the snow and it kept me comfortable," one reviewer commented, adding, "Also wore them on days when I was both in and out and my body quickly acclimated to the climate I was in at the moment." These bottoms can be machine washed and tumble dried.

  • Available colors: 12
  • Available sizes: X-Small – X-Large