9 Best Merino Wool Base Layers

Base Layers - the bread and butter of any layering system. Insulation weight, fit, and material are some factors to consider in your decision. Fortunately, we have tested out the best merino wool base layers around. This article lists the best available options today and helps clear the air about what to look for in your merino wool base layer.

These reviews are focused on merino wool base layer tops. However, most tops have matching bottoms which you will see in some of the reviews below.

Best Merino Wool Base Layers

Smartwool Merino 150 and 250

Material: 100% merino wool

Insulation Weight: Light- to Midweight, 150 g/m² to 250 g/m²

Price: $85

Why we like it: Smartwool is always releasing new colors and fun patterns.

Smartwool's Merino 150 fabric is the perfect weight - not too heavy and not too light. It is ideal for three-season usage and works great as an underlayer for active winter sports. The company also sells a Merino 205 line, which is made with thicker wool that performs best as an underlayer in the winter.

Smartwool is known for its colorful and creative clothing. No matter your taste in clothing, Smartwool has a color, pattern, or style to suit you. For tops, you can choose between tank tops, short-sleeve shirts, long-sleeve shirts, or a 1/4 zip crew. Smartwool makes matching bottoms and even a one-piece top and bottom combo. Also, Smartwool has a 2-year satisfaction guarantee.

Icebreaker 200 Oasis

Material: 100% merino wool

Insulation Weight: Lightweight, 200gm

Price: $95

Why we like it: With over 20 years of history working strictly with merino wool, Icebreaker has set the standard for merino wool quality and function.

Icebreaker is known for their quality clothing and its commitment to sustainability both in the source of its materials and how their clothing is made. A slim-fitting base layer, the Icebreaker 200 Oasis series is ideal for hiking and sleeping in colder temperatures. Icebreaker offers the Oasis in a variety of styles including crew tops, zippered tops, and bottoms. 

Icebreaker spends some time on the design of their clothing The Oasis shirt has offset shoulder seams that reduce chafing when you are wearing a backpack. It also has a drop tail hem that prevents the shirt from riding up and exposing your back to the elements. Another favorite is the legless bottom that stops above the boot and won't add any uncomfortable seams around your ankle.

Meriwool Midweight

Material: 100% merino wool

Insulation Weight: Midweight, 250g/m2

Price: $60

Why we like it: A no-frills straightforward approach using 100% merino wool.

Meriwool stands out for its affordable pricing. All of its base layer clothing costs well under $100. Meriwool tops have a comfortable fit that you can wear either as a standalone shirt or a base layer. The bottoms are equally as comfortable for use during any cold-weather activity or sleeping.

Minus33 Chocorua

Material: 100% Australian merino wool, interlock knit

Insulation Weight: Midweight, 230 g/m2

Layer weight: Size Large = 9.6 oz

Price: $70-90

Why we like it: Minus33 strikes the perfect balance between price, fit, and being 100% merino wool.

Warm and comfortable is how we describe the Minus33 Chocorua baselayer top. Clothing from Minus33 is made from superfine Merino wool that is softer than most merino wool clothing. The Chocorua has a roomy fit that isn't too baggy nor too skin-tight. It’s perfect for wearing as a base layer in the winter or night-time camp clothing during the spring and fall. It has a drop-tail hem to keep your back covered and a regular fit that provides plenty of room.

Combine it with a pair of Kancamagus midweight bottoms and you've got yourself an awesome midweight base layer.

Minus33 Ticonderoga

Material: 100% merino wool

Insulation Weight: Lightweight 170 g/m2

Price: $70-85

Why we like it: A lighter version of the Chocorua, an inexpensive base layer that can be worn off-trail.

Minus33's base layers never disappoint, and the Ticonderoga is no exception. At 170 g/m2, the Minus33 Ticonderoga is slightly warmer than traditional lightweight base layers. It is great for spring and fall hiking or to keep warm on chilly summer nights. 

The Ticonderoga is a regular fit crew-neck that pairs nicely a pair of Saratoga lightweight bottoms. Note that if you prefer tighter fits, then consider getting one size down. 

Woolx 230 Midweight

Material: 100% merino wool

Insulation Weight: Midweight, 230 g/m²

Price: $100

Why we like it: Exceptionally soft merino makes it the coziest base layer on the list.

WoolX is known for its super soft merino wool that never itches and feels as soft as cashmere. The company sticks to the basics with solid colors and the standard styles you’d expect for an underlayer. It looks and feels like long underwear and isn't a layer you could wear outside of camp. Though simple, the clothing is quality made with non-chafing flatlock seams, cuffs to keep pants and sleeves from riding up, and has a slim, athletic fit. Its line of midweight base layers (including their base layer pants) is warm enough for spring, fall, and winter.

Outdoor Research Alpine Onset

Material: 83% merino wool, 12% nylon, 5% spandex

Insulation Weight: Midweight

Price: $50-$100

Why we like it: The spandex is an excellent touch in activities with lots of movement like climbing or ski touring.

Outdoor Research Alpine Onset series takes the best of Merino wool and mixes it with nylon and spandex for flexibility and durability. The layer fits comfortably - it's not too tight, not too loose, and moves when you move. The nylon and spandex also help to hold the shape of the garment through repeated washings. The Alpine Onset clothing gets high marks for its breathability. It is a midweight layer suitable for active sports in the winter, short walks in the fall, and sleeping in a wide range of temperatures. The Alpine Onset bottoms come separately and feature a functional fly.

REI Co-Op 185

Material: RWS merino wool

Insulation Weight: Lightweight

Price: $70

Why we like it: It has a bit of a more relaxed fit so you can wear it at those après sessions at the end of the day without feeling like you are in your underwear.

The REI Co-op 185 base layers are made in accordance with the Responsible Wool Standard and are produced in a Fair Trade factory so you can feel confident about where your base layers are being made. At 185 weight, it hits that sweet spot and is great for just about anything. If you are looking to check multiple boxes with one base layer, this is the one.

PATAGONIA CAPILENE AIR

Material: 5.6 oz. 51% merino wool/49% recycled polyester

Insulation Weight: Midweight

Price: $129

Why we like it: The textured material and unique weave makes it the most breathable base we tested.

Patagonia’s latest addition to the Capilene base layer lineup is the Capilene Air.  It’s unique in the fact that is 51% merino and 49% synthetic, which makes it super stretchy.  As with all things Patagonia, they are very conscious of their impact, they abide by the Responsible Wool Standard and use recycled polyester for their synthetic blend.  It looks and feels like a lightweight sweater, and you can pull it off as one too.

If you are looking specifically for a warm weather, high output layer, the Capilene Cool is a better option.  The 100% synthetic option is more durable and better at moisture wicking due to the flat-weave material. 

Merino Wool Base Layer Considerations

Merino wool clothing is pricey and there are several factors you should consider before handing over your hard-earned cash. We outline the most common features you will encounter and provide some buying advice so you can purchase the correct base layer for your needs.

FIT

Base layers do their magic by managing moisture and keeping your body temp regulated.  To do this, they must fit properly.  Too baggy and it won’t effectively wick moisture away, too tight and it will feel constrictive.  An ideal fit is nice and snug but not too tight where it’s compressing you.  

Every company is going to have their own unique fit and style.  For example, the REI Co-op 185 and Patagonia Capilene Air are both going to have more of a sweater fit, while the Arc’teryx Rho LT and WoolX 230 are both more of a trim performance fit.

Weight

Most merino wool garments are categorized by fabric density. You'll often see it classified as a number such as 150 or 250; it refers to the number of grams of merino wool in every square meter of fabric. These densities are then used to classify the clothing as lightweight, midweight, or heavyweight. The weight you choose depends on the type of activities you do and when you do them.

Ultralight (less than 150 g/m2): Ultralight merino is a great option when you're hiking in the heat. It will help you keep both sweat and odors to a strict minimum while also shielding your skin from the sun.

Lightweight (between 160 and 190 g/m2): Lightweight merino wool base layers can be worn all year round. They're not too hot and not too cold. You can wear them alone in warm temperatures or underneath a jacket when the weather gets cool. Also great for sleeping.

Midweight (between 195 and 250 g/m2): You’ll want a midweight merino layer for the cold winter months. It's a perfect base layer for snowshoeing and skiing. As temperatures fluctuate from below freezing to above freezing, you can easily add or remove outer layers and stay comfortable with your merino 250 base layer at the core.

Heavyweight (greater than 250 g/m2): You'll want to wear a heavyweight merino base layer when you are standing or sitting outside in cold temperatures for any amount of time. These dense layers are great for ice fishing, hunting, or other similar low-key activities.  A heavyweight merino wool base layer may be too warm for strenuous activities such as hiking or climbing.

Material

From 100% merino garments to synthetic blends, the material being used is going to perform differently based on the ingredients.  Merino fibers offer the highest weight to warmth ratio but are more delicate than synthetic fibers.  While synthetic fibers are stronger and stretchier.  

The most common synthetic fibers being nylon, spandex, and polyester.  Nylon is added for strength/durability, spandex is added for stretch, and polyester is added for quicker drying.  

A lot of base layers now use a blend of merino and synthetic fibers, with the best blends using a core-spun fiber.  The wool is wrapped around synthetic fibers, so the merino is against your skin but has a stronger synthetic core.  Keep an eye on the proportions too, you will start to lose the advantages of merino as you get down below 80%.  

Different activities are going to be better suited to different materials.  If you are climbing, a higher amount of synthetic fibers will help keep the shirt from wearing out too fast.  If you are skiing or using it when sleeping, it’s not going to see the same kind of wear and tear so 100% merino is the best.

Style

Most merino wool clothing, especially base layers, are designed with a slim fit that feels comfortable under clothing. There is a wide range of clothing styles that you can mix and match depending on the prevailing weather conditions.

For the harsh temperatures of winter, long-sleeve tops or zippered shirts can be paired with long underwear-style bottoms.

In milder conditions, you can pair a zippered long-sleeve shirt with lightweight leggings or even ¾ length Capri-style pants. Once summer hikes, you don't have to ditch your beloved merino wool. You can wear a pair of merino wool underwear under your shorts and match it with a lightweight short-sleeve crew for a breathable, wicking, odor-free outfit.

Comfort

Since it will be up against your skin, look for flat seams in any base layer to avoid chafing. Ideally, there should be no zippers or buttons. Opt for elastic waistbands and flap-style openings instead.

Most merino wool clothing is designed for active lifestyles and will include convenience features such as a hood, thumb holes, and pockets. A flap-style fly is helpful for the men to use the restroom.

MERINO SOURCE

It has become increasingly important to ensure that the merino wool of your base layer has been sustainably sourced. You can do this is by purchasing from brands that ensure that no animal cruelty has occurred in the sourcing of their merino wool.

Some brands have had their merino wool certified as sustainably and ethically sourced. Some certifications to look out for are ZQ Merino Standard, Global Organic Textile Standard (GOTS), and The Responsible Wool Standard. Some brands will also source their wool from countries like Australia and New Zealand that have strict laws on wool sourcing.

Benefits of Merino Wool

Merino wool is a natural fiber harvested from Merino sheep. Though Merino sheep originated from Spain, almost 80 percent of merino wool now is obtained from sheep raised in Australia and New Zealand. Merino wool is the gold standard for base layers because of its has many desirable qualities.

ODOR RESISTANCE: Merino wool is naturally resistant to odor-causing bacteria thanks to its ability to manage moisture. Without moisture, odor-causing bacteria cannot multiply and cause your wool shirt to stink. Because of its odor-control properties, merino wool clothing doesn't need to be washed as frequently as cotton or synthetic fabrics. When hiking, I can wear merino wool socks for up to a week and t-shirts for three days before washing.

BREATHABILITY: Merino wool fibers are among the most breathable and moisture-wicking fabrics available. Each strand can absorb up to 30 percent of its weight in moisture; wicking it away from your skin and out towards your surrounding environment. As a result, the fabrics feel cool and dry against your skin even when you are sweating up a storm.

UV PROTECTION: Merino wool naturally protects your skin from the sun's damaging rays. Most wool clothing has a UPF rating of 30+ or higher.

QUICK DRY: Merino wool is inherently quick dry without any treatment or coatings.  It dries so quickly because it doesn’t absorb water the way other materials do.  Unlike cotton which can absorb over 25 times its own weight, merino wool absorbs less than half of its own weight.  Meaning, there is a lot less water to dry.  Having dry clothing is critical and we can’t always escape getting wet, so having a base layer that will rapidly dry is essential.

LIGHTWEIGHT: Not all fibers are created equal. Merino wool offers the best warmth-to-weight ratio.  Compared with other fibers and materials of the same weight, merino is simply warmer.  This means you can have a much thinner, lighter garment and won’t have that bulky feeling when you have multiple layers on.  

HOW TO WEAR YOUR BASE LAYERS

Wearing base layers typically falls into three different categories, so think about how you will use them when deciding which one to go with.

Sleeping—From thru-hiking the Appalachian Trail to fall evenings around a campfire, base layers are the ultimate sleeping outfit.  Wearing base layers in your sleeping bag is an essential part of your sleep system.  Go for a trimmer fit to get the most out of your base layers.  Since they are essentially the world’s best pajamas you don’t need to have t-shirt styling and can focus strictly on comfort and performance.

Part of a Layering System—Layers, layers, layers.  The layering system is the key to comfort and base layers are the foundation of the system.  Picking the right base layer for layering is the first step when choosing your layering system.  Nicely fitted base layers will allow you to layer on top without feeling excess fabric bunching up or constricting your movement.  In the winter it’s likely you will always have multiple layers on so a trim fit base layers will work better.  In the warmer months, it’s common to take your mid-layer off once you get moving so a more casual fit is a better choice.

Daily wear—Base layers are incredibly comfortable, so it’s very common for them to be used as the trusty hiking shirt.  If you plan to wear your base layer as a standalone shirt, go for a more relaxed fit.  A lot of base layers are disguised as a t-shirt.  Companies like Icebreaker and Smartwool offer tons of fun colors and designs so you can use the same base layer on trail as you would in town.

FAQ

Do you wear underwear under your base layer?

Wearing underwear under a base layer comes down to personal preference and your hiking conditions. Some people always prefer to have an underwear layer, while others don't like that extra bulk.

We recommend wearing an underwear layer when you anticipate removing layers because of exertion or rising temperatures. If you do need to remove your base layer, then you'll want underwear underneath, or else you'll have to go commando. If it is cold, and you know you won't be shedding layers, then feel free to leave the underwear at home.

How to wash a merino wool base layer?

Merino wool should be washed on a gentle cycle with cold or lukewarm water. Avoid hot water because it causes the wool to shrink. Use a mild soap and do not add bleach or fabric softener as they both degrade the wool fiber. Air dry the wool garment by laying it flat as hanging it may cause it to stretch. If you must use a dryer, then use a low heat setting.

Are merino wool base layers worth it?

Yes.  No other material offers the same kind of performance as merino wool.  Try a pair on and you will immediately notice the difference.  We understand merino wool is expensive, so if you can only afford one set go for something in the midweight range and a more casual fit.  You will quickly find you won’t ever want to take them off.

Should I pair my base layer top with a bottom?

If you are using them for sleeping clothes or part of a winter layering system—yes.  Everything we discussed about base layer tops can be applied to bottoms.  The only exception is that bottoms don’t see the same kind of wear and tear so you don’t have to focus on a pair that are exceptionally durable. Bottoms are more commonly used in colder environments under another pair of pants, or for sleeping in.  Almost all base layer tops have corresponding bottoms, so if you found the perfect shirt there is probably a perfect pair of pants too. 

Other base layer options?

If merino wool simply isn’t in the budget, synthetic base layers are still a good option.  They won’t be quite as warm and will start to smell if they aren’t washed frequently but can still offer good moisture-wicking and quick-drying properties.  Polyester base layers are the best synthetic options, a bit of spandex will help keep it stretchy too.  Fleece is an example of polyester, with microfleece being a decent base layer option for colder climates.

⏭ Read next: Hiking Clothes 101 | What to Wear from the Appalachian Trail

📸 Some photos in this post were taken by Ross Enlow (@rossaenlow)