Merino Wool vs Cotton: The Real Differences, Without the Jargon

How we compared the two fibres

This is not a laboratory report. We read what the wool industry publishes and what independent textile researchers have measured, and set both against years of wearing the two fibres in ordinary life. Two caveats matter before anything else.

First, construction counts almost as much as fibre. A loose cotton poplin shirt and a dense cotton sweatshirt behave like two different materials, and the same goes for a fine merino jersey knit and a chunky merino jumper. Second, blends blur the picture: a sock that is part merino, part nylon is neither one thing nor the other. Where it matters, we say so. These are the seven criteria we used:

• Warmth: how well each fibre holds heat in the cold and when conditions change.
• Moisture: what happens to the fabric, and to you, once you start to sweat.
• Odour: how much body smell each fabric keeps after a day of real wear.
• Feel: softness against bare skin, and the recurring question of itch.
• Care: washing temperature, drying, and the risk of shrinking or felting.
• Lifespan: how each fibre ages under repeated wear and washing.
• Everyday sense: accessibility, availability and the garments where each fibre simply belongs.

Warmth: why merino copes better with changing weather

Both fibres keep you warm in the same basic way, by holding still air close to the body. The difference lies in how well each keeps doing it as conditions change. A merino fibre is naturally crimped; the Woolmark Company likens it, under the microscope, to a fine coiled spring. That crimp gives a knit its loft, the small pockets of air that do the actual insulating.

Merino is also fine. Woolmark puts it generally below 22 microns, against 50 to 100 for a human hair, which is why a merino knit can be thin and still warm. Our dictionary entry on merino wool goes further into the fibre and the breed.

You will often read that merino regulates temperature. The phrase oversells a little. What wool does is buffer: it takes up the moisture vapour your skin gives off before it condenses into sweat, so the air trapped next to you stays drier, and dry air insulates far better than damp air. Dry cotton is perfectly warm. A heavy cotton sweatshirt on a crisp, dry afternoon is a pleasant thing. It is when effort, rain or a sudden drop in temperature enters the picture that the two fibres part company.

Sweat and damp: the difference you feel after an hour

This is the criterion that settles most outdoor arguments. According to the Woolmark Company’s research summary on odour and moisture, wool can absorb up to 35 per cent of its own weight in moisture and takes up about twice as much water vapour as cotton. Those are industry figures, and they describe vapour rather than a bucket of water, but they match what the skin reports.

Cotton behaves differently. It loves water. It draws liquid sweat in readily, spreads it through the fabric and holds on to it, and a wet cotton knit collapses: the air pockets fill, the fabric sticks to the skin and starts pulling heat away from it. That is the heavy, chilly feeling at the top of the hill.

One correction to a popular shortcut. Merino is often said to dry fast. Compared with cotton, a thin merino jersey does tend to feel dry again sooner, but a thoroughly soaked wool jumper is in no hurry either. Its real advantage is that it takes much longer to reach the soaked stage, and feels far less clammy on the way there.

Odour: a real gap, but smaller than the marketing suggests

Merino’s reputation for staying fresh is the claim most often repeated, and the one most worth unpicking. The wool industry’s explanation is that the fibre absorbs odour molecules during wear and releases them in the wash. Woolmark also cites a New Zealand sensory study in which wool fabrics kept, on average, 28 per cent less body odour intensity than cotton, and 66 per cent less than polyester.

Read those two numbers side by side. The large gap is with synthetics, not with cotton. Independent work points the same way: in a 2007 University of Otago study published in the Textile Research Journal, polyester fabrics rated high for odour intensity, while cotton and wool both sat in the mid-to-low range. The same researchers found bacterial counts after one day were similar on all the fabrics. The difference in smell, in other words, did not come down to wool simply killing bacteria, which is how it is usually put.

In practice, a merino T-shirt can often be aired overnight and worn again, sometimes for several days, where a cotton one tends to go into the wash after a day of real activity. That is genuinely useful, on a trip especially. It is a difference of degree, and a worthwhile one.

Softness and itch: what your skin actually notices

Many people who say they cannot wear wool are remembering a scratchy school jumper. The prickle usually comes from coarser fibres whose ends press into the skin instead of bending away. Fine merino bends. Worn next to the skin, a good merino jersey feels closer to soft cotton than to a traditional knit. Sensitive skins still vary, though, and one piece is a wiser first step than a drawer full.

Cotton needs no such introduction. It is smooth, familiar and unproblematic against the skin, and its quality varies mostly with the length of the fibre: long-staple cottons spin into finer, smoother yarns, which is why a good cotton jersey feels almost silky where a cheap one feels dry. For anyone who simply dislikes the idea of wool, cotton remains the obvious, and very comfortable, answer.

Care and lifespan: where the effort goes

Here cotton takes the lead, and clearly. Its fibres actually gain strength when wet, a well-documented property of cellulose, which is why cotton has long been the fibre of towels, bed linen and work shirts that go through hot washes week after week. It can shrink in its first washes if it was not pre-shrunk, and dark colours fade, but it forgives a great deal.

Wool asks for more attention. Every wool fibre carries tiny surface scales, and under heat and agitation those scales lock into one another: the fabric felts and shrinks, and there is no undoing it. Hence the cool wool cycle, the gentle detergent, drying flat and away from the radiator, and no tumble dryer unless the label says otherwise. Wool also loses some strength when wet, another reason to handle it gently at that stage. The compensation is that merino needs washing far less often. Much of its care is simply a night on a hanger by an open window.

Lifespan depends on weight and use more than on fibre alone. A lightweight merino T-shirt, the subject of our guide to merino wool T-shirts made in Europe, can pill or wear through at points of friction if treated like a gym shirt. A cotton jersey tends to thin at the collar and slowly lose its shape. Looked after, both last for years.

Where cotton genuinely wins

It would be easy to write this comparison as a slow lap of honour for merino. That would not be honest.

In dry heat, a loose woven cotton shirt, poplin or seersucker, lets air move across the skin and is hard to beat, provided you are not exerting yourself. For anything washed often and hot, from bed linen to tea towels, cotton’s tolerance of the machine is decisive. Structured fabrics such as denim, canvas and twill have no real woollen equivalent for daily wear. And cotton is generally the more accessible and more widely available fibre, which matters.

It is also, in part, a European crop. According to the European Commission, Greece accounts for about 80 per cent of the EU’s cotton area and production, and Spain, mainly Andalusia, for around 20 per cent. Regenerative farming is starting to change how some cotton is grown, a subject our dictionary entry on regenerative cotton explores.

Merino wool vs cotton: which one for which use

Rather than a verdict, a working rule. Choose merino when you will move, sweat or meet changing weather. Choose cotton when you will stay put, stay dry or wash often. The table applies that rule to common garments and situations.

For the coldest months, the question becomes less merino or cotton than how much merino, and in which weight. Our guide to merino wool base layers made in Europe looks at weights, micron counts and the makers who knit them close to home.

What the fibre label does not tell you

A label reading 100% merino or 100% cotton tells you how a garment will behave. It says nothing about how it was made. A large share of fine merino starts life far from Europe: the Woolmark Company states that Australia provides 81 per cent of the world’s superfine wool. Cotton, as seen above, is grown in Europe only in modest quantities.

For both fibres, then, made in Europe usually refers to what happens after the shearing or the harvest: spinning, knitting or weaving, dyeing, cutting and sewing. Those are the steps that decide how evenly a jersey is knitted, how a seam sits and how long a garment keeps its shape. If you want to know where they took place, our guide on how to identify fashion made locally in Europe explains which words on a label carry weight, and which do not.