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Merino wool – the functional fibre in detail


At the end of the 1980s, many outdoor fans considered functional clothing made of synthetic fibres to be the ultimate products – after „normal“ wool and cotton had become obsolete due to their “unsuitability”. At that time only a few pioneering companies in the outdoor sector such as Icebreaker, Smartwool, Woolpower and Ortovox were using merino wool. Nowadays however, almost all outdoor clothing manufacturers offer products made from this „new wool“. The merino sheep has become the favourite animal of many sports and outdoor enthusiasts. Once you have worn merino wool clothing, you will not want to go without it again. But what is so special about this natural high tech fibre? In the following we will take a closer look at merino wool and its properties:

Where does merino wool come from?

Alles wissenswerte zu Merinowolle
You have to be a sheep…

Merino wool is a natural product obtained from sheep’s wool – indeed, from the wool of merino sheep. The animals originally come from the North African plateaus of the Atlas Mountains and are now among the oldest and most hardy sheep breeds in the world. merino sheep lived there in extreme, often adverse weather conditions of the kind you only get when you spend all four seasons up in the mountains. They had to – and still have to – withstand extreme temperature fluctuations of minus 20 to plus 35 degrees in the Southern Alps of New Zealand. That’s why they have a coat, which is perfectly adapted to such harsh conditions. In the Middle Ages the sheep reached Spain, where their wool was sold as valuable “Spanish wool”. In the 18th century, the first merino sheep were exported to Australia, which has since become the largest global exporter of this precious commodity, along with other wool-producing countries such as New Zealand, South Africa and South America.

What are the properties of merino wool?

Merino wool has a number of natural and very beneficial properties:

  • It doesn’t itch.
  • It warms when it’s cold.
  • It cools when it’s warm.
  • It warms when wet.
  • It does not develop unpleasant odours even after being worn several times.
  • It is water and dirt repellent.
  • It is particularly lightweight with a high heat output.
  • It has natural UV protection.
  • It does not accumulate electrostatic charge.
  • It’s flame-retardant.
  • It doesn’t crease.

These are all excellent qualities when it comes to producing functional clothing for outdoor activities. First let’s look at the most important features in detail and find out why merino wool has these properties.

Why doesn’t merino wool itch?

Merino sheep belong to a breed of fine wool sheep. The coat of these sheep is made up of very fine, soft and highly curled hairs with a fibre thickness of only 16.5 to 24 microns (the fibre thickness of wool fibres is expressed in microns; 1 micron corresponds to 1 micrometre, i.e. 1 thousandth of a millimetre). This means that the fibres of merino wool are only about half as thick as „normal“ wool fibres and only a quarter as thick as a human hair. The finer the wool fibres are, the more they bend when they touch the skin. While thicker wool fibres hardly bend at all, merino fibres curl with up to 40 directional changes per centimetre. As a result, the nerve endings of the skin are much less irritated and there is no unpleasant itching. The human sensitivity limit, above which fibres are perceived as scratching, is around 25 microns. This is why normal wool is perceived as scratchy, while merino wool feels pleasantly soft against the skin.

How does merino wool warm when it’s cold?

Alles wissenswerte zu Merinowolle
Perfect when it’s icy!

Merino wool has excellent insulation properties in cold weather. This is due to the ingenious structure of the merino fibres. The fibres of merino wool consist – in relation to their total volume – of up to 85% air. The fine, wavy fibres lie so loosely on top of each other that air chambers can form between them. And as air is a poor conductor of heat, it provides excellent insulation – against both cold and heat.

The effect is comparable with double-glazing on windows. The air between the two panes has an insulating effect – both in winter and summer. Merino wool is not warming itself, but it prevents body heat from escaping by enclosing insulating air cushions. It keeps the heat of our body where we need it when the ambient temperature is cold. In addition, the merino fibres have fewer contact points with the skin due to their strong wave and therefore dissipate less heat. In a nutshell: the advantage of the curled fibres of merino wool is that more insulating air is bound in and less heat is emitted.

How does merino wool cool when it’s warm?

The human body has a natural air conditioning system. In warm temperatures or during intensive physical activity, we start to sweat. The body secretes moisture in the form of sweat to cool down and keep the body temperature at a constant level.

Merino wool supports this natural bodily function perfectly. It functions like a second skin, which further enhances the cooling effect. On the one hand, the air cushions in the merino fibres insulate not only against cold but also against warm ambient air. And on the other hand, the fibres behave uniquely towards moisture. The level of moisture management that they achieve has never been reached with any artificially developed textile fibre. The fibres of merino wool can absorb up to a third of their own dry weight in moisture – for synthetic fibres, the value is less than ten percent. The fibres owe their high moisture absorption capacity to their chemical structure. They are hygroscopic, which means they can bind moisture in the form of water vapour, and they can do so in great quantities and very quickly. Sweat or rainwater is quickly transported to the inside of the fibre through a network of tiny channels.

At the same time, the fibre surface remains dry because it is water-repellent. This is why merino wool still feels dry even when it has absorbed a lot of moisture. Amazing, right? The hygroscopic fibres function like a storage tank that optimally balances the moisture fluctuations in the environment.

Alles wissenswerte zu Merinowolle
merino wool offers amazing moisture transport.

Evaporative cooling

Warm ambient air now ensures that the moisture absorbed inside the fibre evaporates on the outside of the garment. However, for the process of evaporation – i.e. the transition from a liquid to a gaseous state – the water molecules need energy. They extract these from the nearest ‘body’ – the merino fibres – in the form of heat. The fibres cool down, causing the skin and the body to cool too. This process is called evaporative cooling, and it causes a pleasant cooling sensation on the skin.

Synthetic fibres, on the other hand, can store almost no moisture in their interior. This results in a particularly rapid transport of moisture to the outside. This causes a build-up of heat and the body reacts by increasing sweat production to induce cooling. Of course, this needs correspondingly more energy, which is then no longer available for performance – for example during sporting activities. Studies at the University of Graz have shown a higher lactate increase in athletes who wore synthetic fibre textiles. All in all, the natural function of merino wool also contributes to a higher physical performance – what more could you want?

How does merino wool warm even when it’s wet?

Compared to cotton or synthetic fibres, merino wool retains its good material properties well even when wet. Unlike a cotton T-shirt, a merino shirt does not stick unpleasantly to the skin when it gets wet. And in a sweaty merino garment, you don’t experience any unpleasant shivering either, as you would when you take a break on the summit in a synthetic T-shirt. But why?

Ultimately, this warming effect in a moist state is also based on the ability of merino fibres to absorb moisture. When moisture is absorbed, an exothermic process takes place, which generates absorption heat. That means that the fibres heat up when they absorb moisture. Sounds incredible, right? But it’s true! Merino wool actively warms as long as it absorbs moisture. This is because the protein molecules of merino fibres release energy in the form of heat when they come into contact with water molecules – enough to cause a temperature increase of up to ten degrees, depending on the quality of the fibre.

Dry clothing at the beginning of the tour

This process continues until the wool fibres are saturated with water molecules. A slightly damp merino base layer can therefore generate heat, whereas a layer that is completely soaked from the rain cannot. But even then, the merino part still keeps warm – due to the frictional heat of the fibres that is generated mechanically during movement. But, with light rain it actually makes sense to wait a short time before putting on a waterproof jacket. If the merino T-shirt gets slightly wet, it will start producing warmth.

The warming process works best if the merino functional clothing is completely dry beforehand, because then the fibres can best exploit their potential for absorbing moisture. It is therefore sensible to completely dry the garment before starting an outdoor pursuit – especially in winter. This is best done in a warm room with the lowest possible humidity, such as a room heated by a stove or central heating. Spare clothes made of merino wool should be packed in a waterproof stuff sack or a plastic bag before your trip, so that the wool fibres cannot absorb moisture from the ambient air. After all, you only want them to warm up when you put them on!

Why doesn’t merino wool smell even after wearing it several times?

The unpleasant smell that we often perceive on ourselves and our clothes is not actually sweat. Fresh sweat is odourless. We first start smelling when the skin bacteria begin to break down the sweat into its individual parts. Sweat provides nutrition for them, and they like to multiply especially in warm and humid regions – like the armpits. Of course, sweat and skin bacteria also settle in our clothing, so these – at least if they are made of synthetic fibres and do not have an odour-inhibiting treatment – will also start to smell unpleasant at some point. So why are garments made of merino wool different?

Synthetic fibres have a smooth surface to which sweat and bacteria can adhere particularly well. Merino fibres have a scaly surface, almost like a tiled roof. The bacteria don’t stand a chance. In addition, the fibres absorb the moisture of the sweat so quickly that the bacteria do not even have time to break down the sweat. The water-repellent fibre surface also prevents the development of a humid climate, which the bacteria need to grow.

Alles wissenswerte zu Merinowolle
Warms even whet damp.

Antibacterial effect

Finally, wool fibres have a specific fibre protein (like all animal hair) – keratin – which breaks down the bacteria responsible for the bad smell. Merino wool therefore has a natural antibacterial effect – and its permanent, because the effect doesn’t weaken. Even the silver ions incorporated in synthetic fibres, which are intended to inhibit odours, cannot match this ingenious biological function. But that’s not all! To perfect this mode of action, merino fibres also have a mechanical self-cleaning effect. This is because the core of the fibres consists of two different cell types that can absorb different amounts of moisture. This means that they swell unequally when absorbing moisture. This results in constant friction, which the fibres use to continuously clean themselves.

Why is merino wool water and dirt-resistant?

Even though merino fibres can absorb relatively large amounts of moisture, their fibre surface is water and dirt repellent. This is because the fibre contains the wool grease lanolin. When the wool is processed, a large proportion of this is washed out, but some remains on the fibres. The wool grease acts as a protective layer. Dirt and odours stick to the fibre surface and can’t penetrate inside. Lanolin can also have a pain-relieving effect on rheumatic joint complaints, which is why people who suffer from this like to wear woollen clothing. Due to the strong curling of the fibres, water drops only have a very small surface area to attack and simply roll off due to their surface tension. This works in exactly the same way as with certain plants, which have fine hairs on the surface that ensure that water drops roll off.

Merino wool in the outdoors – are there only pros? Or are there cons too?

We’ve probably spoken enough about the advantages of merino wool in the outdoor sector. For all the reasons mentioned above, it should be clear this “high-tech wool” is particularly well-suited to outdoor use. In summary, merino fibres are true all-rounders that do what is needed in every situation – they warm when cold, they cool when warm, they warm when wet, they do not develop any unpleasant odours and last but not least they feel pleasant on the skin. With this flexibility, merino wool garments are naturally perfect for outdoor activities. Because no matter whether it’s warm, cold, wet or dry outside – when you’re outdoors, you need clothing that is just as flexible as the weather we’re exposed to.

Temperature and climate-regulating properties

Above all, the temperature and climate-regulating properties of merino wool are a huge advantage in many outdoor situations. The body temperature always remains at a comfortable level despite different temperature conditions and different activity levels. And these are common conditions – especially in the Alps. Changes in the weather or temperature play a major role when you’re covering hundreds of metres in altitude. You might be sweating in the valley, but once you start rising up to the breezy ridge, you’ll start to shiver. And when you need to take a break at the summit, a material which can warm when wet is invaluable. The temperature-regulating wool is also ideal for activities such as cycling, ski mountaineering and skiing, where activity levels and temperature conditions vary greatly as you go up and down the mountains.

The odour-retardant property of merino wool is particularly beneficial when you are out and about for long periods and aren’t able to wash. On a trekking tour or backpacking trip, where you are travelling with the least possible weight, you’ll want to take merino clothing which can be worn for an unlimited period of time. After all, it takes quite some time until they smell strong enough that you feel the need to wash them. And thanks to the elastic fibres, a merino shirt won’t crease much even if it’s squashed into your backpack for days on end.

Disadvantages of the wool

Basically, there are almost no limits to the use of merino wool garments in outdoor activities. Whether you’re a keen trail runner, climber, yogi or just want something for everyday wear – the material is simply great. However, there are a few disadvantages that should be mentioned. Merino fibres are not as robust or resistant to wear and tear as other natural or synthetic fibres.

If you wear a pure merino wool T-shirt under a heavy backpack, it might damage the fabric. If weight and pack size are your most important considerations, synthetic fibre garments usually perform better. They also usually dry faster. Sometimes clothing made of pure merino wool can feel too warm in summer despite their cooling properties. And last but not least, there are particularly sensitive people who find that merino wool is itchy.

However, the outdoor textile industry has now found possible solutions to eliminate these disadvantages of merino wool – by using fabric blends.

What types of fabric blends are there?

Alles wissenswerte zu Merinowolle
Ideally put your clothes on when as dry as possible.

The current outdoor trend is to combine merino fibres with other natural fibres such as silk or synthetic fibres. Synthetic fibres include polyamide and polyester, but also synthetic fibres that are artificially produced from natural cellulose – such as Lyocell or Modal. This allows the strengths of the natural and synthetic fibres to be combined to get the best of both worlds. Different materials are used depending on the manufacturer and application.

For example, Icebreaker adds a small amount of elastane to its merino base layers. This is not a classic blended fabric, but a sandwich construction that ensures that only pure merino wool lies next to the skin. The addition of elastane makes the fabrics more tear-resistant and durable, as the fabric can stretch more under mechanical stress instead of tearing. As even finer wool fibres can be used in this way, the fabric feels more comfortable, especially for sensitive people, than fabrics made of pure merino wool. At the same time, the fabric has a pleasant stretch effect as well as a mostly body-hugging fit.

Lyocell fibres with merino wool

Ortovox and Icebreaker also offer collections which use Lyocell fibres together with merino wool. Lyocell is the generic fibre name for a fibre made from bamboo wood. It is marketed by the Austrian fibre manufacturer Lenzing AG under the brand name Tencel. The addition of Lyocell or Tencel gives the fabric a pleasantly cooling effect on the skin, which is of course particularly beneficial in summer. The Lyocell fibres have a particularly high basic moisture content, which does not feel wet but cooling on the skin. Furthermore, the material is more durable and long-lasting.

Modal, for example, is used by Ortovox to complement merino wool. Modal is made of beech wood cellulose and has a particularly smooth surface. As a result, Modal fabrics feel very soft and have a silky feel. It is especially loved by those with sensitive skin.

Falke and Engel produce outdoor clothing with a mix of merino wool and silk. These textiles also feel very soft and pleasant on the skin. Silk also gives the garments a shimmering sheen.

If you choose garments made of blended fibres, however, you should look carefully: blended fibres can be used for two reasons: either to improve the functionality of the material or to reduce costs by using a cheaper material. If the proportion of merino wool is too low, the good properties of merino wool fibres are then lost somewhat.

How sustainable is merino wool?

When it comes to sustainability, it is also worth taking a closer look when buying a product. On the one hand, merino wool is by nature a very sustainable material. On the other hand, however, there are certain problems in animal husbandry, which are among the unpleasant aspects of wool production. But first of all, let’s look at the advantages of merino wool in terms of sustainability.

Alles wissenswerte zu Merinowolle
A merino sheep in Tasmania

Merino wool is a naturally renewable raw material. Merino sheep can be sheared up to twice a year and produce up to ten kilograms of wool per animal. Furthermore, compared to the production of synthetic fibres, the production and processing is particularly low in resources and environmentally friendly. Synthetic fibres are produced using crude oil, which requires a large number of chemicals and the use of large amounts of energy. Moreover, synthetic fibres are almost completely non-degradable. Synthetic clothing takes 30 years or more to decompose.

This means they end up in landfill after use. Products made of pure merino wool, on the other hand, are biodegradable without any residues. You can just throw them on the compost heap. A merino T-shirt buried in the ground will completely decompose within 90 days and can then be used as fertiliser. Furthermore, merino wool has natural properties such as odour inhibition, so it doesn’t need any environmentally harmful chemical additives. This is because the „technology“ is already contained in the fibre. Last but not least, the self-cleaning function of merino fibres also protects the environment, as the garments do not need to be washed as often.

Animal welfare

However, animal welfare is not always the top priority in merino wool production. In Australia and New Zealand, there is an issue with fly maggot infestation in merino sheep farming, which can cause the deadly disease, myasis. The animals are virtually eaten from the inside. In warm temperatures, such as those found in the Australian summer, the flies lay their eggs in the poorly ventilated skin folds on the anus, which are smeared with faeces and urine. In Australia – the country with the most merino wool producers – a brutal method is unfortunately used to prevent fly maggot infestation – mulesing.

This involves surgically removing a plate-sized part of the skin folds around the anus, tail and vulva of lambs up to eight weeks old. This is usually done with a hot cutting device, without anaesthesia and while the sheep is fully conscious! The wounds are not treated, but must heal and scar by themselves.

Great pain is inflicted upon the animals during this bloody and mutilating procedure. Studies show that the sheep still flee their tormentors 113 days after such an operation – that’s how traumatic this experience is. At present, there are very few uncontroversial alternatives to solve the problem of fly maggot infestation. Particularly because the fly maggots were probably – just like the merino sheep – only imported to Australia and New Zealand during the colonial period. More complex and expensive methods include regular shearing of the skin folds around the anus, regular checks of the sheep and timely medical intervention in case of infestation. Animal welfare activists therefore demand the targeted breeding of sheep with fewer skin folds on the buttocks. In fact, Australian merino sheep were deliberately bred to have more skin folds and thus a higher yield of wool.


In view of these gruesome facts, when buying a merino product you should consciously make sure that only mulesing-free merino wool was used. This is guaranteed by the ZQUE seal of the New Zealand merino industry, for example. Many companies such as Icebreaker or Ortovox also state exactly where they get their wool in a traceable way. Merino wool that does not come from Australia or New Zealand is always mulesing-free, as there is not the problem of fly maggots.

Most outdoor companies such as Icebreaker, Ortovox, Bergans, Woolpower, Smartwool, Rewoolution, Devold and many others do not use wool if mulesing has been practised. If you are unsure, you should contact the manufacturer or dealer. If a merino garment is a very reasonable price, it may be due to the practising of mulesing. It is worth taking a closer look and maybe spending a little more. In return, you’ll get flawless quality and support the species-appropriate keeping of merino sheep.

How do I wash merino wool?

We wrote a detailed article on how to care for merino wool. Nevertheless, we would like to give you a brief overview. You can wash merino wool at 30-40°C using a wool detergent, but without fabric softener. However, please make sure that the wool detergent does not contain any enzymes. The enzyme protease is responsible for breaking down the keratin in the merino wool. This causes the wool to break down and form holes. If you are unsure, it is better to use a pH-neutral mild or functional detergent, then you will be able to enjoy your merino wool for longer.

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