Merino vs. Polyester - Which should you choose?

There are three main types of material used in clothes we wear today: cotton, synthetics (polyester, nylon) and wool. Each material has its benefits, so sometimes it's hard to choose. Not sure which one is right for you? Keep reading and find out! 


For performance wear, cotton is the least appropriate of the three. Though it is nice to the touch and 100% natural, it’s a relatively heavy material and it absorbs a lot of water. A cotton t-shirt that is drenched in sweat will stay wet for hours on end. Not only that. When wet, it will feel clammy against your skin and keep you drenched in water that is trapped in the cotton fibers. Cotton also loses all insulation qualities when wet, so it will not offer any warmth at all.


Synthetic materials, especially polyester, although made of plastic fibers, offer quite a few benefits over cotton. Polyester is a very lightweight material, extremely durable and dries faster than any other. This is due to the fact that it absorbs practically zero water. All excess water will therefore simply drip off of the fabric and only the water trapped on its surface will need to dry off. 

But if it doesn’t absorb any water, doesn’t that mean that it also won’t let any water out, trapping moisture on your body when you sweat? The answer is: “Yes, it used to.” And that is why people used to prefer cotton. However, in the last decades, polyester fabric technologies have advanced immensely. It is now much softer to the touch, more breathable and generally nicer to wear. This is why cotton has all but disappeared from performance wear. 

There is, however, one negative aspect of polyester fabric that still remains. Wear it for hours on end and it will start to smell. The reason, again, is due to the fact that it is essentially made out of plastic fibers. On top of the smell, it will also start accumulating bacteria which can irritate your skin and cause health problems if you wear it for extended periods without washing. 


You won’t find merino wool in general-purpose sportswear brands like Nike, Under armour and the like. The reason is simple. These brands are focused on activities that usually don’t last more than an hour (a gym session, game of basketball, a run, etc). For that one hour, polyester based fabrics are more than good enough. However, outdoor activities such as hiking or climbing last many more hours, sometimes even days. That is why brands that are focused on outdoor activities started choosing merino over polyester. 

First of all, what is the difference between wool and merino? Merino is a specific type of wool that comes from Merino sheep. So all merino is wool, but not all wool is merino. Merino wool is much thinner, “milder” and more adaptable than “regular” sheep wool. That makes it much nicer to the touch. The main reason why people don’t like to wear wool is because it tends to itch. Think about wearing your grandma’s itchy Christmas sweater against bare skin. Not so nice! But because merino wool fibers are much thinner than regular wool, it’s more flexible and it bends softly against your skin, which means it doesn’t itch one bit.

Merino wool is naturally antimicrobial so those nasty bacteria won’t build up in the fabric even after days of use. And it won’t smell. Honestly! You can wear it while hiking 8 hours a day, multiple days in a row and it won’t develop any odor. The only odor you might acquire is the B.O. - your body odor. But that’s a different story. 

There is another quality of merino that is the reason it’s called the miracle fabric. It doesn’t lose insulating properties when wet. A wet merino shirt will still keep you as warm as a dry one. And when it’s wet, it doesn’t stick to your skin like cotton or polyester, so you don’t feel like you’re wet at all.


By this point, we’ve established that cotton is no good for adventures outdoors. 

If you’re serious about outdoor clothes, it comes down to polyester and merino. However, there is no clear winner between the two and you need to choose based on some specifics.

Comfort: winner (tie)


Modern premium polyester fabrics, while not made out of natural materials, feel airy and soft. With an emphasis on modern and premium. Your 20 dollar Nike t-shirt is not made for a full day of hiking and won’t feel nice. A premium polyester shirt made for outdoor activities, on the other hand, will. 

Merino is as soft (if not more) as polyester and more breathable. However, it’s still wool and a small (unlucky) percentage of people might be slightly allergic to it and they will feel itchy while wearing it. If you’re not among those, wearing merino will feel awesome!


Warmth: winner (merino)


In general, warmth comes from the thickness of the fabric. The thicker the fabric, the warmer it is. At the same thickness, polyester will provide slightly more warmth. However, as soon as your shirt gets slightly wet, merino will continue to keep you warm, while with polyester, you’ll freeze your butt off. 

Especially in winter, that is a huge advantage. Imagine going uphill and breaking a sweat. With polyester, you need to be very diligent about removing a few layers before you get too hot, start sweating and makemakie your polyester shirt wet. With merino, you don’t have to worry nearly as much. Your merino base layer can get very sweaty and it won’t matter. You’ll still be warm. 

And it’s not just about sweat. If you accidentally get wet due to rain or snowfall, merino will still offer you thermal protection while polyester will not. 


Drying time: winner (tie)


Cotton absorbs the most water, merino absorbs much less than cotton, while still some, and polyester absorbs almost no water. Therefore, in theory, polyester wins this one. However, as mentioned earlier, with merino, it really doesn’t matter much if it gets wet. And while it might take slightly longer to dry than polyester, it won’t stick to your skin or chaf and rub like polyester. So it won’t feel like you’re wearing a wet shirt at all.

Breathability: winner (merino for a base layer, polyester for a mid-layer)


If we compare similarly thick merino and polyester fabric, merino is the undisputed winner. However, if we want to make a really thick merino fabric, it needs to be very dense. The increased density reduces breathability. If you’re looking for a mid-layer (which is thicker than a base layer), polyester will be the way to go, but for a thinner base layer, merino will provide far more breathability. 


Odor: winner (merino)


It’s not even close. Merino. 


Durability: winner (polyester)


Everybody knows plastic is more durable than natural materials (which also makes it less environmentally friendly). Unless you snag your shirt on a very sharp rock, it won’t rip. And even with a lot of chaffing and rubbing, it won’t tear. 

Merino is more delicate. You just can’t weave wool tight enough to make it durable. Every fabric made out of wool, including merino, will over time start to tear at the seams (armpits, neck, shoulders, waist). It will be much more prone to wear and tear withwhen a rucksack or your climbing harness rubbingwill rub against it. Even washing it too often will start to make the wool thinner and weaker. Conclusion: you can have 20 year old polyester shirts, you can’t have 20 year old merino shirts. 


Weight and size: winner (polyester)


Merino is heavier than polyester. However, the real issue is not just that. Merino clothes tend to be thicker than polyester to make up for the lack of durability compared to polyester, which can be extremely thin and still very durable. An extremely thin merino will tear in a heartbeat, so merino fabric will tend to be slightly thicker. 


However, as we’ve established, merino won’t develop any odor or trap bacteria. This means you can wear the same shirt multiple days in a row and one merino shirt is much less weight in your backpack than 3 polyester ones.


Sustainability: winner (merino)


While some polyester fabrics are recyclable, they are still essentially plastic made from oil. Merino is 100% natural. It’s sheep hair.

Price: winner (polyester)


The cheapest polyester is far cheaper than any merino. However, you wouldn’t want to wear a cheap polyester shirt for a 10 mile hike while wearing a backpack. So it’s not a fair comparison. The polyester that is used in clothes for outdoor activities (especially hiking and climbing) is more expensive and so the price gap compared to Merino is not as big. Nevertheless, merino is still more expensive, which is hardly surprising given that it needs to grow on sheep.

Overall winner


If we exclude the cheaper, more gym oriented polyester sportswear and compare only the more premium polyester fabric suitable for outdoor activities and merino, it’s difficult to say which is overall better. It really depends on the specific situation. 


In our opinion, merino is definitely the superior fabric in winter. Especially for a base layer (unless you are one of the unlucky few who really can’t wear wool on your bare skin and polyester is the only choice you have). Having merino as a base layer, it won’t matter much if you get it wet, either from breaking a sweat or by weather factors. And because in winter, we usually wear a mid-layer over our base layer and an outer layer on top, your merino base layer won’t directly rub against the straps of your backpack or get caught in branches or a sharp rock and so durability won’t be much of an issue. 


In summer, things are more complicated. People tend to think wool is only used in the cold, but they couldn’t be more wrong. Merino is an overall great thermal regulator. It will keep you warm in the cold and keep you cool when it’s hot. However, you will want to wear a thin merino shirt in summer and that will come at the price of durability. For a short hike, polyester might be the way to go. But for a very long or even a multi-day hike, especially when you need to pack light, a good merino shirt will be the perfect companion. 


In short:

For winter hikes, we recommend a merino long sleeve base layer. 

For high intensity or shorter activities (autumn or winter runs, cross country skiing) we would recommend our Summit Long Sleeve tee, which provides more breathability.

For summer: go with a polyester t-shirt for shorter hikes and choose a lightweight merino t-shirt for longer and multi-day hikes. 

For mid-layer: choose a grid-based fleece from polyester for activities and a wool fleece for leisure wear. 

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