Functional Underwear: Merino Wool vs Synthetic Fibers

Functional Underwear: Merino Wool versus Synthetic Fibers

Temperature-regulating, perspiration-transporting, insulating – our expectations of functional underwear are high. But which fiber meets these demands best: merino or synthetic? We have compared the advantages of both materials.

Functional Underwear

Functional underwear should be breathable and quick-drying, protect against overheating and cold, and thus provide its wearer with a comfortable body climate during all sporting and sweaty activities.

There are products made of natural fibers and synthetic fibers on the market, all of which have different advantages.

To make it easier to decide among the large selection of functional underwear and baselayers, we have compiled the essential properties of merino and synthetic fibers.

Outdoor underwear merino

Fine wool from merino sheep

Merino wool belongs to the fine wool and comes from merino sheep, most of which are native to Australia, New Zealand or South Africa.

Clothing made of merino wool is available in a wide variety of designs: From 100 percent merino to blended fabrics in combination with spandex or with polyamide.

An attempt is made to combine the advantages of merino wool with those of synthetic fibers.

Merino wool is ideal for tours where you can’t change clothes as often because you can’t carry as much weight or because washing options are limited – such as trekking, hut touring or backpacking trips.

You can wear a shirt made of merino wool for several days without scaring away fellow hikers and travelers with the smell of sweat.

Merino Sheep

 * Disclosure: Links marked with Asterix or some picture links on world’s-finest-wool are affiliate links.  All our work is reader-supported – when you buy through links on our site, we may earn an affiliate commission. The decision is yours – whether you decide to buy something is entirely up to you.

Properties of merino wool

  • Moisture absorption: Wool attracts water vapor and can absorb about one-third of its mass in moisture without feeling clammy. Despite the fiber’s moisture retention, the fiber surface is water repellent, so the material feels dry.
  • Thermal insulation/breathability: thanks to the numerous air pockets inside the crimped fibers, wool provides excellent insulation against the cold, even when wet. The air pockets also contribute to rapid moisture removal and temperature regulation. Thus, merino wool warms when it is cold and cools when it is warm.
  • Skin-friendliness: merino fibers have a much thinner diameter, unlike conventional virgin wool, which is why merino fibers do not scratch. The fine merino wool is exceptionally soft and, therefore, contrary to the assumption that wool scratches, very comfortable to wear.
  • Odor: Merino wool has an antibacterial effect. The bacteria can hardly stay on the wool fibers’ scales, which is why the laundry does not develop an unpleasant odor even after extremely long wear.

Merino Wool and Sustainability

Merino fabrics are a natural raw material that regrows and is 100% biodegradable without residues. Wool is part of the natural carbon cycle, as fifty percent of wool weight is pure organic carbon. 

Merino Wool is also the best recyclable fiber. As is the case with cotton, no fertilizers or pesticides are needed for production, and no fossil raw materials such as crude oil are needed, as is the case with synthetic fibers. 

But we need to admit; even if it is a renewable product, its production impacts the environment. Wool also needs energy, water and chemicals to turn the raw material into a textile fabric.

In wool’s ecological footprint, the relatively high water consumption during washing the wool and the dyeing and carding process is most significant. 

Sustainable Fashion


Synthetic fabrics

Synthetic fibers can basically be divided into two types. There are human-made fibers from natural polymers that are chemically processed. These include, for example, fibers made from cellulose, such as viscose and modal, from which primarily thin, silky fabrics are made.

These are comfortable against the skin but less robust.

The second group is pure synthetic fibers made from synthetic polymers such as polyamide and polyester. Synthetic functional underwear is usually made from these two fibers or blended fabrics, often combined with spandex.

Some manufacturers use recycled polyester in the manufacturing processes to make their products more environmentally friendly.

Polyester Yarn Manufacturing Process

Characteristics of synthetic fibers

  • Moisture absorption: Polyester and polyamide hardly absorb any moisture, but they can transport it away from the body remarkably quickly thanks to textured cavities in the yarn so that the underwear remains dry even during high exertion.
  • Thermal insulation/breathability: Special spinning processes are used to vary the insulating properties. Depending on requirements, there is functional underwear where the main focus is on moisture transport or thermal performance.
  • Skin-friendliness: Textiles made of synthetics are particularly suitable for people with very sensitive skin, as only fine, soft polyamide and polyester fibers are used, ensuring an extremely comfortable feel.
  • Odor: Synthetic fibers have a smooth surface on which bacteria can adhere better, which is why they smell faster. Additional chemical treatment can prevent odor formation.

Synthetic fibers and sustainability

Synthetic materials and sustainability? At first glance, this seems to contradict each other. But is natural fiber really always the better, more sustainable choice?

We took a closer look to explain what sustainable synthetic materials are and what you should look for when buying outdoor textiles.

Polyethylene Terephthalate (PET) and Recycled Polyester

Polyethylene Terephthalate – or simply PET – is the most common type of plastic and the basis for polyester. Newly produced polyester is definitely not a sustainable option for outdoor textiles, as it is made from precisely this PET and is based on increasingly scarce fossil oil.

More and more companies are turning to recycled polyester, which can also be recognized by the abbreviation rPET. In this process, “old” plastic is melted down and spun into new fibers.

The advantages: Plastic that is no longer used is reused and doesn’t end up in landfills or, even worse, in the ocean. The production of rPET is also much more resource-efficient than new production – with almost the same quality.

Sustainable Outdoor cloth
Some manufacturers of outdoor clothing use recycled polyester

ECONYL® - a fiber made from plastic waste

The goal behind Econyl yarn is: producing new products from nylon, but without wasting resources or even using crude oil. How does it work?

The Italian manufacturer Aquafil collects nylon waste from landfills and oceans around the world. Old fishing nets, carpet cuttings, industrial plastics and fabric scraps are transformed into the “regenerated” nylon Econyl.

It is just as valuable as newly manufactured nylon but can be recycled, recreated, and reshaped repeatedly. So for every 10,000 tons of yarn, 12,600 tons of waste are recycled.

Econyl is fine, yet robust and tear-resistant, making it an ideal sustainable alternative for polyamides, often used in outdoor textiles. In the outdoor apparel industry, the manufacturer Prana is using this innovative fiber.

prAna - Women's Pillar Capri

prAna Women's Halle Straight-Short

prAna Women's Halle Pant


This very soft and easy-care fabric is considered semi-synthetic because the base material is cellulose: a natural substance obtained from wood. However, the cellulose is then chemically transformed, so viscose is known as artificial silk.

In textiles, viscose is popular because it absorbs moisture and is as comfortable to wear as cotton. Viscose is based on the renewable raw material wood. Besides, no petroleum is used in its production. Pesticides are also primarily not used in cellulose cultivation.

But there are also downsides: The viscose process requires a lot of energy. Unfortunately, the chemicals used also pollute the environment.

Even though viscose often performs better than fully synthetic fabrics, the disadvantages weigh heavily. If you value sustainability, you should therefore look for alternatives.

Regenerated fibers: Modal and Lyocell

These two semi-artificial fibers are also made of cellulose. They are produced from naturally occurring, renewable raw materials such as bamboo and other wood types via chemical processes.

Modal usually comes from native beech trees. When buying, it is best to make sure that the fabric comes from particularly sustainable forestry – because then you have a higher certainty to hold environmentally friendly manufactured modal in your hand.

Lyocell or Tencel® is the most sustainable synthetic fiber; it is also made from eucalyptus wood. The fabric is soft and absorbs moisture while being very durable and breathable.

The fiber is biodegradable, and only a few chemicals are needed for its production. Even the used chemicals are recycled again in a closed-loop. Another advantage: eucalyptus trees grow quickly and do not require pesticides and hardly any water during growth.

Regenerated Fibers




Part of the outdoor textile industry has recognized the enormous environmental impact caused by the production of textile fibers and is striving for more and more synthetic fibers produced sustainably.

It is not always possible to say that natural fibers are the better and more sustainable option.  Even with natural fibers, a lot of energy, chemicals and materials are used for cultivation and further processing – which is also reflected in the environmental balance.

Merino wool or synthetic fibers?

Merino wool shows its strengths especially in functional underwear – it is pleasantly soft, does not scratch and insulates well:

Merino underwear is especially suitable for more extensive tours because it remains odorless even after prolonged wear. So you need less change of clothes and can save space and weight in your luggage.

Besides, merino wool offers exceptional wearing comfort due to its fine fiber structure and excellent temperature regulation. Merino underwear is available in different thicknesses, so you do not have go without merino comfort even in summer.

Functional underwear made of Synthetic Fibers is especially impressive for its fast drying time and high tear and abrasion resistance.

The soft fibers are particularly skin-friendly and thus ensure a high level of wearer comfort. Special technologies can also be used to create additional effects such as an odor-preventing effect or a cooling effect on the skin.

What is your opinion about the role of wool garments and Regenerated Synthetic Fibers in a Sustainable Fashion Industry? Feel free to leave us a comment!

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