Hiking Gear Merino Wool

Merino Wool Base Layers: Lightweight But Warm Merino Wool Long Sleeve Shirts

October 23, 2021
Ibex Merino Wool Base Layer

Staying warm during the winter months starts with a good base layer. These merino wool base layers are comfortable, lightweight, and excellent at keeping you warm and dry.

If you’re still trying to figure out the secret to staying warm when it’s cold outside, it’s all about the layers. And not just many you have or how thick they are, but what they are made of.  

I am a huge fan of merino wool. I wear merino wool t-shirts during the warm months, and layer up with wool during the winter, starting with a lightweight merino wool base layer.

Merino wool is super comfortable, sustainable, and its unique characteristics work to keep you cool in warm weather, and warm in cold weather.  
How to layer merino wool for winter

1 Start with a thin, breathable merino wool base layer. A base layer is first and foremost meant to keep you dry by wicking moisture away from your body.

2 Add a second layer for warmth. A midweight second layer should trap in the heat.

3 The outer layer adds additional warms and keeps you dry from the elements, like rain or snow.  

Looking for other posts about merino wool? Read more here:

Waterproof Barefoot Winter Boots

Start with a merino wool base layer to stay warm on a snowy day

FAQs about Merino Wool as a Base Layer


Is merino wool the best base layer?

Merino wool, wool blends, and synthetics all perform well as base layers for cold weather. You may be able to find a synthetic base layer with performance similar to a merino wool base layer, but synthetics are made from plastics, use large amount of chemicals in production and emit toxic waste. In contrast, merino wool is natural, sustainable and biodegradable.

There are companies that work towards making sustainable and environmentally friendly synthetic clothing, but it’s hard to beat a natural fiber like wool. Buying and wearing merino wool base layers instead of synthetics is just one small way I can protect the natural world that I love so much.  

However, there are many other reasons merino wool makes the best base layer. Wearing wool means you don’t have to sacrifice performance to be environmentally conscious. Here are the amazing properties of merino wool:

Comfort: Merino wool is super soft and feels amazing as a next-to-skin layer. Merino wool fibers are finer and softer than your typical wool, which has given this fabric a bad rap in the past for being itchy. I’d opt for a merino wool t-shirt everyday over cotton or synthetics simply for how nice they feel. [[link to merino wool t-shirt here]

Odor-resistant and naturally antimicrobial: This means it can (usually) handle multiple wears without being washed.  

Moisture-wicking and breathable: This makes it good for both warm and cold weather.

Durable: In fact, it’s eight times stronger than cotton. Because of wool’s naturally crimped fibers, it can stretch without losing shape. My merino wool clothes and base layers still look almost new after years of wearing and washing.

Are merino wool blends as good as 100% merino wool?

In order for a fabric to maintain the essential properties of wool, aim for at least 80% merino wool. Blending merino wool with a nylon or polyester core can reduce costs and actually make the fabric more durable, all while keeping the warmth and moisture-wicking capabilities of wool. Blends with lower percentages of wool can still make great base layers. Just note that if a fabric isn’t mostly wool, it may not deliver on the  amazing promises of merino wool listed above.

Is merino wool the warmest fabric?

Merino wool is warmer than other fabrics relative to its weight. Merino wool is incredibly efficient at locking in heat, which means a merino wool base layer will keep you warmer than a synthetic if they’re both the same weight (basically thickness) of fabric. This means even thin merino wool base layers do an excellent job of trapping your body heat in and keeping you warm.

Should base layers or thermals be tight?

Merino wool base layers should be fitted. They should be comfortable and easy to move in, but if they’re a bit baggy or loose, those layers will not be as efficient at keeping the warmth in and the cold out.

What does the weight or GSM mean in terms of merino wool?

When shopping for merino wool layers, you may see that many of the shirts include a number in the title, like 150. This number refers to the grams per square meter, often written as GSM or g/m2. This is the weight of the fabric. The lower the number, the lighter weight the fabric. When you’re looking for the best merino wool base layer, thicker isn’t better. Two lightweight wool layers will keep you warmer than one thicker one. A base layer is meant to be a breathable layer that wicks moisture away from the skin, so keep it light.  

Lightweight (150 to 180 GSM): Base layers are usually made of lightweight merino wool fabric that is 150 to 180 GSM. This versatile fabric can be worn all year, and is also great for lightweight merino wool tees meant for warm weather.

Midweight (190 to 250 GSM): This fabric is a bit thicker and is often used as a mid layer. It can also be used as a base layer in very cold weather. Some merino wool tees for hiking and warm weather are also made with this midweight merino wool.

Heavyweight (260 to 320 GSM): This heavyweight merino wool can be used as a midlayer or only layer in cool weather. As a denser knit, it doesn’t breathe as well as a lighter base layer, so it’s better for when you’re going to be sitting or standing outside, not intense activity.

Outerweight (330 GSM and up): This fabric is meant for outerwear weight, often seen as felted wool coats.  

Is merino wool worth the price?

Merino wool clothing is expensive. And if it’s a base layer, no one’s likely going to see it, so it’s not like you’re trying to make a fashion statement. Merino wool base layers are more of a performance statement, and if you’re going to be in cold weather, they’re totally worth it. With proper care, merino wool layers can last a long time. For sustainably, warmth, and durability, I’ve found merino wool base layers and clothing to be worth it.

Where can I find a great deal on merino wool clothes?

Even if merino wool is worth the higher price tag, that doesn’t mean you shouldn’t look out for a great deal. We check for sales on Backcountry and REI (Black Friday and Cyber Monday usually have the biggest discounts). Discount websites like Steep & Cheap (which is owned by Backcountry), Mountain Steals (owned by Moosejaw) and REI Outlet also have good deals. The selection is much more limited, but if they do have something you’re looking for (like a merino wool base layer!), then you can buy it at a deep discount (like 50% or more).

If you want to know how to keep your wool in the best shape plus tips for storing in the offseason, see the merino wool care guide at the bottom of this post.

Lake Helen at Lassen Volcanic National Park

Best Merino Wool Base Layers


1 Icebreaker Merino 175 Everyday Long Sleeve Thermal Top

  • Material: 100% Merino Wool
  • Insulation Weight: Lightweight 175 GSM  
  • Retail: $85

I think of Icebreaker as the OG merino wool clothing company. Jeremy Moon launched the brand back in 1995, on a mission to make high quality outdoor and natural performance clothing without using petrochemical fibers. All of Icebreaker’s clothing are made from merino wool, with a range from ultralightweight merino wool base layers to thick knitwear.

Icebreaker’s Merino 175 Everyday Long Sleeve Thermal Top is a simple, versatile staple you’ll be wearing all winter long. The women’s version features a scoop neck, which is something I look for in a base layer after having thermals with higher necks stick out from underneath sweaters. The men’s version of this wool thermal top comes in a crew neck. The slim fit makes these easy to layer.

Shop Women’s: Icebreaker, REI, Backcountry | Shop Men’s: Icebreaker, REI, Backcountry

Icebreaker Lightweight Wool Base Layer

2 Ibex Woolies Tech Long Sleeve Crew

  • Material: 81% Merino Wool 12% Nylon 7% Elastane
  • Insulation Weight: Lightweight 180 GSM
  • Retail: $105

Ibex is another company that has been perfecting outdoor performance merino wool clothing for over two decades. They not only use sustainable materials (wool), but also work with their supply chain to reduce their carbon footprint wherever possible, offsetting the rest as a climate neutral company. You can be assured that your Ibex clothing is coming from sheep and people that are treated ethically with their wellbeing at the forefront.

Ibex offers both men’s and women’s merino wool base layers. The Ibex Woolies Tech Long Sleeve Crew is a lightweight merino wool thermal made with a nylon core for added strength. The added elastane gives the fabric some stretch. The fabric is so soft and comfortable!

They have a few fun color options beyond the standard black and grey, and look chic enough as an only layer in warmer weather.  

Shop Women’s | Shop Men’s

Ibex Merino Wool Base Layer

Ibex Merino Wool Base Layer

Ibex Merino Wool Base Layer

3 Isobaa Merino Long Sleeve

  • Material: 100% merino wool
  • Insulation Weight: Lightweight 180 GSM
  • Retail: $105 | Discount code KELLY 25 for 25% off

Isobaa’s 100% merino wool shirts are some of the softest I’ve ever felt, and all come from non-mulesed sheep. Isobaa’s focus on sustainability is notable throughout its supply chain, all the way down to the packaging. My merino wool base layers arrived in recycled and recyclable brown paper and cardboard. It can be a little frustrating for a sustainable product to arrive in plastic packaging, and I really appreciate the effort Isobaa has made to create a fully sustainable supply chain.

Isobaa’s merino wool base layers are designed with a few thoughful details that make them so comfortable. These 100% merino wool long sleeve shirts feature flatlock stitching to reduce chafing, offset shoulder seams to prevent rubbing from backpacks, and an underarm gusset panel so there aren’t any annoying seams in your armpit.  

Shop Men’s | Shop Women’s

Isobaa merino wool T-shirt
Long-sleeve merino wool t-shirt by Isobaa

4 REI Co-op Merino 185 Long-Sleeve Base Layer Top

  • Material: 100% merino wool
  • Insulation Weight: Lightweight 185 GSM
  • Retail: $79.95

REI Co-op gear is usually great quality at a great price, and the 100% merino wool base layers are no exception. These long sleeves feature flat seams to eliminate chafing and underarm gussets for easy arm movement.

Shop Men’s | Shop Women’s

REI Coop Merino Wool Base Layer

5 Smartwool Merino 150 Base Layer Long Sleeve Top

  • Material: 87% merino wool/13% nylon
  • Insulation Weight: Lightweight 150 GSM
  • Retail: $85

Smartwool’s 150 base layers have a slim fit with raglan sleeves. This is helpful if you’re wearing a backpack as the seams are offset from any straps. This fabric is a merino with a nylon core for added durability.

Smartwool also carries this long sleeve in a 250 weight, which makes a great merino wool mid layers or a thicker base layer for when you won’t be very active outdoors.

Shop Men’s | Shop Women’s

Smartwool Merino Wool Base Layer

6 Unbound Merino Men’s Long Sleeve Merino Crew

  • Material: 100% merino wool
  • Insulation Weight: Lightweight 190 GSM
  • Retail: $95

Unbound Merino is a men’s merino wool clothing company that launched with the goal of creating a simple, hard-working but good-looking travel wardrobe for men.  

Unbound’s clothes are designed to help you pack and travel light, and look put together in almost any situation. The Long Sleeve Merino Crew is lightweight 100% merino wool, and looks great as an only layer while also performing well as a base layer.

Unbound ensures the quality, sustainability and ethicality of their supply chain by using  Woolmark and RWS (Responsible Wool Standard) certified merino wool.  

Shop Men’s Unbound Merino

Unbound Mens Merino Wool Long Sleeve T Shirt

7 Proof 72-Hour Merino Long Sleeve Tee

  • Material: 87% merino wool, 13% nylon
  • Insulation Weight: Lightweight 180 GSM
  • Retail: $92

Proof makes high-quality, everyday essentials for men made with the best performance fabrics. Proof calls their merino wool long sleeve tee the 72-hour tee because, well, it’s made to wear for 72 straight hours. You can put that claim to the test–and they expect you to. You can check out one of their 72 hour tests (complete with smell tests) here. 

This men’s merino base layer is made from super soft 16.5 micron woo sourced from New Zealand. 

Shop Men’s Proof 72-Hour Merino

Proof Men's Merino Wool Base Layers

8 Kora Yushu Long Sleeve Crew

  • Material: 60% premium Yak wool, 40% merino Wool
  • Insulation Weight: Midweight 240 GSM
  • Retail: $130

The Kora Yushu Long Sleeve stands out on this list because it’s made of a merino wool and yak wool blend. Yak wool touts many of the same properties of merino wool; it’s naturally odor-resistant, breathable, and moisture-wicking. It’s also super soft, right up there with cashmere.  

Yak wool has a few of its own unique properties that keep you extra warm in the cold. After all, this natural fiber has to keep yaks alive in freezing temps up in the Himalayas. Yak wool is super-fine, hollow, and very flexible. All of this means it’s adapted to trap air between the fibers to increase insulation and keep you warmer while also being incredibly breathable. As someone who really loves merino wool, I feel a little traitorous saying this, but yak wool actually warmer, more breathable, and wicks moisture more quickly than the same weight of merino wool. Combining yak and sheep’s wool means you get superior performance out of this fabric.

At 240 GSM, the Kora Yushu long sleeve is more of a midweight layer, so it works great if you find yourself needing a bit of extra warmth in your base layer. It’s also an awesome midlayer.  

Shop Men’s | Shop Women’s


How to care for merino wool clothing

After making an investment in merino wool base layers, it’s important to care for them correctly if you want them to last. Here are a few tips on keeping your wool shirts in great condition.

Rethink Clean and Wash Less: I used to think it was gross if I didn’t wash a piece of clothing after every wear. But this isn’t true. Wool is odor-resistant and anti-microbial properties keep the stink away, so wool clothing can go several wears (or more) without being washed. One way to refresh your wool without washing is to put a worn item in a ziploc bag and place it in the freezer overnight. The low temperatures kill bacteria and will make your clothes feel fresh again. We got this great tip from Nui Organics!  

Use the right soap: One of the worst things you can do to your wool clothes is throw them in the wash with regular detergent. Most laundry detergent is made of enzymes that are designed to break down biological molecules – like food stains. But since wool is also a biological molecule (it’s basically just proteins), laundry detergent will break down the molecules in your wool clothes too. Instead, use a wool-specific wash like euclan.

Handwash: The best way to wash wool is in cold water with no agitation and a wool wash. This wool wash is rinse-free, which makes it really easy to hand wash too. I know some merino wool clothing says it’s machine washable, but personally I always default to a handwash if the fabric is mostly wool. If it’s around a 50% blend (like 50% wool 50% tencel), then I’ve used the gentle cycle on the washing machine without any issues.

Air dry: After gently washing your wool, carefully squeeze them out (don’t twist or wring) and hang them to air dry.  

Hiking through Butano State Park in sustainable outdoor clothing brand Toad&Co


Protect your Merino Wool Base Layers and Clothing during the Off Season

Once spring or summer rolls around, it may be time to pack up your merino wool base layers and store them during the warmer months. Merino Wool clothing is expensive, and it’s no fun pulling them out again to find them full of holes.  

Several pests like cloth moths and carpet bug larvae love organic materials like merino wool. They can eat their way through an impressive amount of clothing relative to their size, so making sure your woolens are pest free before storage is essential. Here are a few tips for prepping and storing merino wool base layers and clothing:

1 Inspect and brush off your clothes. While you may not see any issues and you’ll want to clean your clothes anyway, it’s helpful to see if there are pieces that need some extra cleaning and attention.  

2 Wash. Thoroughly wash wool clothes and base layers to get rid of any sweat or dirt. Smells attract bugs, and bad odors will set in if they’re stored that way. While you may be tempted to put them through a heavy-duty wash on high heat, most wool clothing makers recommend a delicate or handwash in cold water with wool-specific detergent.

3 Freeze. After they’re clean and dry, freezing your clothes for a few days (or weeks) in an airtight plastic bag will help make sure you’ve killed any unhatched pests (yuck, I know).  

4 Air dry. Air them out and make sure they’re fully dry before storage.

5 Airtight Storage. Store them in an airtight container in a cool, dry location. I like these WeatherTight boxes. You can find them consistently online at a few places like The Container Store) and Amazon. I ended up finding them for the best price on Overstock.com, so this is a great option if they have them in stock. They fully seal and have a tight latch, designed to keep out both moisture and bugs.

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