Merino Wool vs Synthetic

One of the most important factors in choosing your outfit for any outdoor activity is the material it’s made of. Most active clothing on the market is made from wool, merino wool or synthetic materials such as polyester. But how do you know which one is right for you?

merino wool vs synthetic materials
In warm weather, you might get away with a thin synthetic top. But when it gets colder, you’ll want to have three principal layers:

The mid-layer and base layer, as well as your gloves, socks and hat, will usually be made of merino wool or synthetics.

What’s the difference between merino wool and synthetic? What about blends?

Merino wool comes from merino sheep and features thinner fibers than regular wool, usually less than 24 microns wide.

Its lanolin coating helps repel water, and it fights smelliness by inhibiting the growth of certain bacteria.

Merino wool is a versatile and effective insulator: it will keep you warm when it’s cold outside and vice-versa.

A note about mulesing:
Mulesing is the practice of removing patches of skin around a sheep’s buttocks to prevent flystrike. This is an inhumane and unnecessary practice; try to avoid buying merino sourced from sheep that have been mulesed. Mulesing is banned in New Zealand but not in Australia.

Synthetics are usually made of a polyester blend, sometimes with spandex, elastane, nylon or polypropylene; different combinations can give different results.

Some synthetics are specially formulated to feel smooth against your skin, others to be effective moisture-wickers, others for optimal insulation, etc.

Many companies also make activewear out of a merino-wool/synthetic blend, touting this as the best of both worlds – the durability and flex of synthetics, plus the odor-control and insulation properties of merino wool.

Blends often come at a higher price point. While blends are getting better and better all the time, some people argue that they are inferior to pure merino or pure synthetic materials as they don’t offer 100% of the advantages of either.

Best moisture-wicking material

Merino wool and synthetics wick moisture in completely different ways. Merino wool regulates your body temperature by absorbing water vapor from your skin and then slowly evaporating it.

Merino can absorb up to about a third of its own weight in moisture without feeling wet to the touch, meaning it’s effective even when you’re sweating heavily or if it’s humid or a bit rainy.

Unlike merino, synthetics are hydrophobic. Instead of absorbing moisture into the fibers, they move it mechanically to the other side where it can evaporate.

While merino naturally adapts to different temperatures, synthetics quickly get wet and clammy – but they dry super-fast.

Does polyester keep you warm?

Polyester fleece is an effective insulator when used as a mid-layer in cold (but not extreme) temperatures. It’s breathable, which is good but means you should combine it with an outer shell to protect against the wind. Wool is a better choice if you expect wet or very cold conditions.

Merino Wool



Wicks wellExpensive
Breathes wellNot as durable (can lose its shape with repeated washing, can get snagged, can shrink)/td>
Insulates well by trapping air between the fibresCan be a problem for those with sensitive skin or wool allergies
LightweightVulnerable to moths
Adapts to different temperaturesSlower to dry
Protects against UV raysInhumane if sheep have been mulesed
Can withstand humidity without feeling wet to the touch
Soft against the skin and less scratchy than regular wool
Naturally stretchy
Renewable, recyclable and biodegradable
Naturally flame-resistant and anti-static




Quick-dryingGets very smelly
Effective moisture-wickerClammy to touch
Durable/easy to care forPetroleum-based so highly flammable
StretchyNot environmentally sustainable
Retains shape better than wool
Cheaper than wool
Good warmth-to-weight ratio
Not itchy
Not as breathable as merino

When to choose merino vs. synthetic

Merino wool is more versatile and is a better choice when faced with rapidly changing temperatures. It also keeps you warmer so it’s the clear choice in frigid conditions. Synthetics can be an attractive option in hot temperatures.

If you sweat a lot, you might want to shy away from synthetic materials as they will quickly start to stink. In contrast, I have worn merino socks for 4-5 day hikes without washing them and they weren’t smelly at all (ask my tentmates!).

When you’re going on holiday for a long time and won’t be able to properly care for your clothes, keep in mind that merino is slower to dry and more difficult to wash.

When to choose synthetic:

  • During prolonged, uninterrupted workouts
  • When temperatures are warm enough that you’re looking for your clothes to help cool you down
  • In dry conditions
  • When you can change clothes often
  • When you want to dry your clothes quickly
  • If cost is a factor
  • If you’ll be scrambling or beating aside blackberry bushes (merino can tear)

Examples: cycling, summer hiking, running

When to choose merino:

  • When you’ll be moving slowly
  • In variable weather
  • When you anticipate being cold (although some synthetics provide good insulation)
  • If you need to wear your clothes for many days without washing them(!)
  • In wet weather (but then bring a shell in case of really wet weather)

Examples: winter hiking, bouldering, and caving, stop-start activities

How to care for merino or synthetic clothes

You can wash synthetics in the washing machine and machine-dry on low heat. Stay away from fabric softeners, which will interfere with the special coatings already on your merino wool or synthetic clothing.

Take special care when washing merino wool as it may shrink or lose its shape – handwashing or gentle machine washing in lukewarm water is the way to go, and always line-dry.

It’s best to wash it as little as possible as it loses integrity every time it’s washed. Watch out for moths, be careful of tears and be sure to darn holes as soon as they appear or they will run.

Alternatives to merino and synthetic materials

    • Silk:
      Silk has an amazing warmth-to-weight ratio, and with chemical treatment, it can even wick moisture. But, it’s not very breathable.
      Since it’s so expensive and delicate, it’s usually reserved for glove and sock/boot liners (or sleeping bag liners).
    • Cotton:
      Cotton absorbs moisture without letting it evaporate. This makes it a useless moisture-wicker at the best of times, and an actual danger when you’re in very cold conditions, as your damp clothing can pose a hypothermia risk.
      Some cotton has been treated to improve its moisture-wicking capacities but it won’t be as efficient as merino wool or synthetics.

There is a range of other materials such as hemp or bamboo that can be an attractive choice for light activity in mild weather.

Ultimately, it’s up to you to decide what material you find more comfortable in different conditions, depending on whether you run hot or cold, how much you sweat, etc. The good news is there’s a ton of choice out there, both in merino wool and in synthetic!

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