Gear Wars: Merino Wool vs. Synthetic Base Layers

I‘m not going to pretend that I can get through a “merino wool vs. synthetic base layer” article without saying “it’s all about that base” at least once. So there, I got it out of the way. Meghan Trainor quotes aside, base layers are one of the most crucial parts of any thru-hiking kit. They can make or break you through a cold snap, and seriously improve your quality of life on trail if chosen carefully.

The two main types of base layers are merino wool / merino wool blends, and synthetic blends. These two different options both feature a wide range of possibilities when it comes to warmth, moisture wicking, and durability. However, depending on the season of your hike and how much you’re willing to invest, each option has its respective pros and cons.

Why Should I Care About Base Layers?

I’m glad you asked. A base layer is the first garment next to your skin, so you want it to be comfortable, moisture-wicking, durable, and somewhat odor resistant. Most thru-hiking and backpacking kits include a versatile base layer top and bottom, unless it’s exceptionally warm and you can get by without tights. You want the garments to fit snug without being restrictive, and comfortable enough to be worn while hiking and to sleep. In the summer months, a lightweight and breathable base layer will provide enough coverage for cool mornings on the trail and nighttime. Meanwhile, trips with more variable weather require mid or heavy-weight base layers that effectively wick sweat away from your body while keeping you warm.

We’re thoroughly covering merino wool and synthetic layers in this article, with a brief mention of silk base layers. The only fabric I will absolutely not allow as a base layer for a backpacking trip is cotton. I learned that “cotton kills” back in my late-teen triathlon days. It basically has no moisture-wicking ability, stays damp for an extremely long time, and is not breathable. Needless to say, we will not be covering cotton as an option.

Merino Wool vs. Synthetic Base Layers

Merino Wool

Merino wool is the soft, non-itchy Australian cousin of regular wool. Although synthetic garments are technically lighter on average, merino wool feels warmer against the skin. And on a perceived warmth to weight comparison, merino wool is king. Many garments now use some sort of merino wool blend, in order to take advantage of merino’s positive properties while still keeping the price tag low. Furthermore, many companies now mix wool layers with different fibers, like spandex or nylon, in order to allow for movement and stretch.


merino wool vs. synthetic

Merino wool vs. synthetic base layers: Nordic skiing in ~30-degree weather with only merino wool top/bottom on. These layers are the Smartwool Intraknit series, PERFECT for high output in extreme cold.

  • Warmth. The structure of merino wool fibers traps heat more efficiently than any synthetic—including when wet. This is why for the same weight, wool or wool blend layers will be warmer.
  • Cooling properties. Merino can be worn in the summer too. Though the price tag may be steep, an ultralight merino wool t-shirt or long sleeve feels like next to nothing for the hotter months.
  • Weight. Because of the warmth-to-weight ratio already discussed, merino garments are often lighter. This makes merino wool tights a great option for camp pants while backpacking.
  • Odor-resistant. Ah, yes. Personally, this is the reason I wear merino layers throughout the winter. Because the merino wool absorbs and dissipates moisture, stink doesn’t build up either. It takes roughly seven sweaty runs before I start to notice a stench in my layers and give them a wash.
  • Breathability. Merino technically retains more moisture than synthetic (see Cons), but in contrast to polyester and nylon, it rarely feels clammy. Merino does a great job staying warm when wet and traps moisture in the fibers, away from your skin.


Merino wool vs. synthetic base layers: not the only whole I’ve torn in a pair of merino wool tights.

  • Not as durable. I take extra care when washing my merino wool base layers, and make sure to use them at least five times before they make it to the laundry. Also, anecdotally, merino wool is more prone to snags and tears. This can be tough on a thru-hike where you may not have total control over how your layers are washed.
  • Pricier. Because of their coveted warmth to weight value, merino wool and wool blend base layers are not the budget option. When you add in the extra care required for these garments, it’s surely an investment.
  • Moisture management. OK, merino is actually still pretty darn good with moisture (pun intended), but it takes longer to dry than synthetics. Remember that merino also does a superior job retaining body heat when wet, at last partially making up for any deficiencies in the quick-dry department.
  • Moths. They will eat your wool clothes, resulting in lots of holes and sadness. Anecdotally, moths seem to prefer lightweight wool to heavier (250g/square meter or thereabouts) weaves.

Sustainability Notes

  • Raising sheep for wool uses precious resources, like water and land.
  • Raising livestock contributes to climate change.
  • Ethical concerns about using animal products in clothing.
  • Sheep are a renewable resource.
  • Many companies are pivoting to more ethical / less impactful wool raising practices.

 Best Use

I recommend merino wool for backpacking or thru-hiking trips where cold temperatures are of concern. It will keep you warmer for less weight, and also hold off that all-too-familiar stench for longer than a synthetic layer.

I wear merino wool for pretty much everything in the winter. Because it handles moisture so well, I don’t have to worry about sweating too much and then freezing later. However, I have a variety of different layers for different activities and temperatures. My Smartwool Intraknit Base Layers are ultra-warm, and best for running or hiking when it’s 20 degrees or lower. I also own a pair of REI’s merino wool layers, which are better for warmer temperatures or under another pair of pants.


Synthetic (polyester and nylon) base layers have a wide range of options. Ranging from budget-friendly layers good for summer months to high-quality winter layers, synthetics are designed for everything. Though they don’t handle odor as well as merino wool, synthetic layers still dry out and wick moisture just as well, if not better.


Merino wool vs. synthetic base layers: underneath my rain jacket is an Arc’teryx Vertices Hoody synthetic base layer. It’s taken a beating, and it’s my go-to for variable conditions

  • Durable. Synthetic layers are less susceptible to tears, snags, pilling, and general wear. Because of this, you can expect to throw these in the wash and have them come out good as new (if you can get the smell out). I brought a synthetic base layer on the JMT, and although it took 3 washes to get the smell out, it still looks brand new.
  • Moisture-wicking. It took me a  long time to understand what “moisture wicking” actually is. Basically, your sweat has an easy time moving through the fibers, allowing the moisture to pass through the garment. For high-intensity activity, this is a crucial feature. Synthetic base layers can be constructed to wick sweat better and dry faster than merino wool.
  • Less expensive. In general, comparable quality of a synthetic base layer is less expensive than wool or wool blend layers.
  • Stretchier. Because they are able to blend different fabrics together, synthetic layers often include spandex or something like it, which stretches to your skin.


merino wool vs. synthetic

Merino wool vs. synthetic base layers: I wore the same Arc’teryx layer on the JMT – and it took more than one (or two) washes to get my special smell out.

  • Less warmth for weight. Although synthetic base layers run lighter than merino on average, they aren’t as warm per ounce. This may not be of the utmost importance on a warmer trip, but for any picky-ounce counter on a colder trip, a synthetic layer would really have to earn its spot in some other way.
  • More smells. Without the odor-resistance of merino wool, next-to-skin layers are sure to take a smelly beating during an intense backpacking trip.

Sustainability Notes 

  • Petroleum-based products required for the production of these garments.
  • Microplastics released when washing these garments (and they require more washing).
  • Synthetic layers are not biodegradable.
  • More durable than merino, theoretically meaning fewer replacements needed.

Best Use

Synthetic base layers are best for clothing you want to last forever, no matter what you put it through. They are great for high output activities, followed by throwing it in a normal wash cycle without worry. So, these are great for thru-hikes. However, because they don’t resist odor as well as merino wool they require washing more often, and may reach the stinking point of no return.

Honorable Mention: Silk Base Layers

Silk base layers are incredible for low key activities, such as a picnic on a winter day or walking your dog on a cold morning. They also have a great warmth to weight ratio, but they are not suitable for backpacking. Because of that, I’m not going to bother going into detail about the respective pros and cons of silk base layers.

Merino Wool vs. Synthetic: Which Base Layer is Best?

merino wool vs. synthetic

Merino wool vs. synthetic base layers: merino wool tights are my go-to for winter running. The top is a synthetic blend, which I like for sweaty runs when it’s not unbearably cold. I’m also wearing merino gloves, my secret weapon.

If your priority is the most warmth possible with the least amount of weight, merino wool is the one. This is best for shoulder season or winter thru-hikes and backpacking trips, where weather is the biggest safety concern.

If your priority is finding an affordable base layer that will last through the ages, I recommend a synthetic option. This is best on trips where you’re expecting to get mighty sweaty, and want a layer that will bounce back when tossed into the wash.

At the end of the day, it comes down to what weather you expect to encounter, and what other layers you have to compliment the base. If you’re planning to bring a large puffy jacket, you may not need the warmest base layer on the market. Conversely, if you’re skimping on outerwear, consider splurging on something you’ll be excited to snuggle into every night.

Base Layers for Every Budget

Okay, so now it’s time to figure out what the heck you’re going to buy. These are a variety of options for buying brand-new base layers, both synthetic and merino. Bear in mind that the merino option for each of these categories is significantly more expensive than the synthetic, for reasons already (overly) hashed-out. And of course, there are always resources for used gear like REI’s used gear website or Patagonia’s Worn Wear.

Budget Option

Merino Wool Option

Synthetic Option


Merino Wool Option

Synthetic Option

Serious Investment

Merino Wool Option

Synthetic Option 

Featured image: Graphic design by Libby Thompson (@libby.des).

Affiliate Disclosure

This website contains affiliate links, which means The Trek may receive a percentage of any product or service you purchase using the links in the articles or advertisements. The buyer pays the same price as they would otherwise, and your purchase helps to support The Trek's ongoing goal to serve you quality backpacking advice and information. Thanks for your support!

To learn more, please visit the About This Site page.

Comments 12

  • Rolf Asphaug : Feb 19th

    Thanks for a comprehensive comparison with good gear suggestions at different price points. I’m thru hiking the Colorado Trail this summer and while I really like my Columbia Silver Ridge Lite long-sleeve shirts, I’ve bought a Wool & Prince merino long-sleeve shirt and will try it out this spring. It’s lightweight (130 weight) and according to W&P is only a little over 4 oz, which is lighter than the Columbia shirt. I’ve heard different stories about whether it keeps you as cool as nylon in hot weather, so I’ll try that out early this summer. If it works for me, I’ll love being a little less stinky when I go into town and meet up with my wife along the trail. PS: While not merino, I love my alpaca Appalachian Gear Co. hoodie, which keeps me toasty in cool weather but somehow also doesn’t overheat me in warmer weather. Thanks again for all of The Trek’s useful info!

  • Jo Cosby : Feb 19th

    Well written article with lots of great facts. I work with sheep and wool and highly recommend anyone interested in the sustainability side of things to simply google “wool as a carbon sink”. Its awesome how we can work with our land and animals to create a closed loop clothing cycle. (I have an old sweater in my compost right now as an experiment!)

  • Al` : Mar 7th

    …..what the heck even is this article.

    Okay there’s a million “merino vs synthetic” articles out there and they all repeat “hiker knowledge” that’s not even true.

    “Merino Is warmer because its warm when wet”: Merino fibers do absorb sweat and allow that sweat to heat up inside. But synthetic wicks and dries so much faster. So this is really down to what you’re doing and what else you have layered. Merino will feel better on your skin when its damp which I guess shouldn’t be undersold. That’s why wool socks are basically standard (because you feet is always a little damp inside a shoe) You can get a bad “flash dry” with a wet poly base layer + a stiff wind. A

    “Merino has cooling properties” No it doesn’t. Companies can defy nature to knit a merino garment thin enough it won’t hold heat. But the ones that are thin enough (140wt or less) have worse durability and still don’t hold a candle to the variety of whisper light polyester sun shirts.

    “Weight” There’s clo-values out there. Regardless a 200wt merino base layer is going to be heavier than a comparable synthetic layer by a few ounces. Its not enough to matter for most people though.

    “Smell” All true with the caveat that 100% merino is the only real king. Odor resistance of merino layers is inverse of the percentage other fibers blended in. Odor treatments have narrowed the gap a little bit, but they mostly only make poly bearable for more than a day and easier to wash (no more “permastink” you’d get with old base layers having a slight sour smell out of the wash).

    “breathability” entirely up to the fabric weave/knit itself, not the material. That said, polyester can be woven into all sorts of textures. The variety of gridded fleece and base layers provide a lot more channels for synthetic fabric to dump excess heat.


What Do You Think?