Affiliate disclosure: some links on this page are affiliate links. If you buy through them I may earn a commission at no extra cost to you. I only link to a brand where it fits the topic, and the claims below come from the sources listed at the end, not from the brands’ advertising alone.
Merino wool is sold as the natural, sustainable answer to polyester. It is soft, it copes with being worn repeatedly between washes, and it does not shed plastic. But search for “is merino wool sustainable” and you will also find warnings about animal welfare, farming emissions and a poor score on one well-known industry index. So which is it?
The honest answer is that merino is neither a miracle fibre nor a villain. It is a farmed animal fibre, so its impact depends heavily on how the sheep are kept, how the land is managed and how long you keep the garment. This guide goes through what the evidence says, who is saying it, and what I could not verify, so you can judge a label for yourself.
The short answer
- Animal welfare: look for a named standard, such as the Responsible Wool Standard, rather than the word “ethical” on its own.
- Climate and land: wool is a farmed fibre and its farming impact is real. Whether it beats synthetics depends on the method of measurement, and brands and researchers disagree.
- Microfibres and end of life: synthetic fibres persist in the environment for longer, while natural fibres are generally expected to break down faster. Detailed wool-specific evidence is mostly from the wool industry itself.
- Durability: a merino garment you wear for years and repair is the most reliable way to lower its impact per wear.
What “ethical” merino means: mulesing and the Responsible Wool Standard
The most common animal welfare concern with merino is mulesing, a practice used on some sheep farms to reduce the risk of flystrike. The sock brand Darn Tough describes mulesing as cruel and says good flock management makes it unnecessary. That is one brand’s view, but it explains why many wool brands now say their wool is “mulesing-free”.
A claim like that is easier to trust when it sits behind a published standard. The Responsible Wool Standard was developed by the nonprofit Textile Exchange. According to Darn Tough’s explanation, it covers sheep welfare, including access to clean water and adequate food and no mulesing, responsible land management such as limiting pesticide use and soil erosion, and the tracing of wool through processing, with restrictions on certain chemicals and a requirement to treat wastewater. It also addresses working conditions for farm and processing workers.
Two cautions. First, Darn Tough says it follows the standard but is not yet certified. It states that around 85% of its sock wool is RWS certified and that the rest is US-sourced wool for tactical socks. Those figures come from the company’s own blog, and I could not find independent audit results to confirm them. Second, I could not read the standard’s full text from Textile Exchange’s site, so I have not listed its exact thresholds. If a brand claims RWS certification, ask for the certificate number or look for the standard’s logo on the product, rather than relying on a general “responsibly sourced” line.
For a wider look at what certification logos can and cannot tell you, see my guide to what sustainable fashion certifications actually mean.
Farming impact: why wool scores badly on some indexes
Here is the part brands often skip. Wool has been rated poorly on the Higg Materials Sustainability Index, which is widely used in the clothing industry. Sheep Inc, a wool brand, has published its own answer. It says the index uses an average impact for the farming industry rather than data from specific farms, and that it measures only the impact from raw fibre up to the factory gate. The brand also accepts that agriculture is a major contributor to the climate crisis.
Sheep Inc argues that farms differ widely and that regenerative farms could reduce impact or even make it positive, and that the index ignores what happens when a garment is thrown away. These are the brand’s own arguments, not independent findings, and I did not find independent research in this search that settles the question. The sensible reading is that wool’s farming footprint is real, that farm-level data matters, and that anyone claiming wool is “carbon negative” without showing the data deserves a sceptical look. My guide to spotting greenwashing in fashion sets out the questions to ask.
Microfibres and what happens at the end of life
Synthetic fabrics such as polyester and acrylic shed tiny fibres when washed. REI’s summary of the research says synthetic fibres resist breakdown in the environment and so may increase in concentration over time, while natural fibres are more prone to breaking down when exposed to the elements. It also says every fabric eventually releases microfibres, wool included, and that researchers are still working out how much is released and what the effects are. That page dates from 2017 with a later update, so newer research may exist that I have not covered.
The wool industry body Woolmark goes further. Its page says wool biodegrades in marine environments and so does not add to microplastic pollution, and cites a study titled “Microfibre Pollution and the Marine Biodegradation of Wool”. The page gives no authors, journal or year, so I could not check the study, and Woolmark is funded by wool producers. Treat it as a claim from the industry, not a settled fact. What can be said safely is that wool is a natural protein fibre, that it is expected to break down more readily than polyester, and that nobody should wash any garment more than necessary.
Be aware of blends, too. Many merino socks and base layers contain nylon or elastane for stretch, which changes the end-of-life picture. My comparison of bamboo, merino and organic cotton socks looks at that in detail.
How to read a merino label
- Fibre content first. 100% merino, or a blend? Check the percentage of nylon, elastane or polyester.
- A named standard. RWS or another recognised scheme, with a way to check it, is stronger than “ethically sourced”.
- Origin and making. Where was the wool grown, and where was the garment made? A brand that cannot say is telling you something.
- What the brand admits. A page that states its limits is usually more reliable than one that claims perfection.
Two brands to look at, and what I could verify
Peregrine is a British knitwear brand. In an interview with TheIndustry.fashion in 2021, its managing director Tom Glover said that 100% of what it makes is made in England, at its own factory in Manchester, and that the business began as J.G. Glover in 1796, with the Peregrine brand introduced in 1956. The article names 100% merino wool for its children’s jumpers and its limited-edition Makers Stitch Aran jumper. The article makes no environmental claims specific to Peregrine, and these statements are the company’s own. If you want to see its range, you can browse Peregrine’s knitwear. It is an affiliate link, and I have not found a sustainability certification for its wool, so check the product page for fibre and origin details.
Danish Endurance sells merino socks among its basics, and I covered what its own page says in my Danish Endurance socks and basics review. You can see its merino and sustainability pages to compare for yourself. Again this is an affiliate link, and the same advice applies: read the fibre mix and the certifications before you buy.
Make merino last: care and repair
Because the best lever you control is how long a garment lasts, care matters. Cycling brand Rapha’s wool care guide recommends following the care label, using a wool detergent, avoiding strong detergents and bleach, avoiding the tumble dryer and drying garments flat. It also suggests airing wool between wears instead of washing it every time and keeping garments away from velcro and rough trims. That is one brand’s guidance, so always follow your own garment’s label first.
For more, see how to wash clothes more sustainably, how to store clothes so they last longer and basic clothes repair. If a pricier merino jumper puts you off, the cost-per-wear guide shows how to compare it with a cheaper one. And for the bigger picture of which brands are worth a look, my honest guide to UK sustainable clothing brands is the place to start.
What I could not verify
- Independent audit results for any brand’s RWS certification claims.
- The full text and thresholds of the Responsible Wool Standard.
- Independent, peer-reviewed data for wool’s farm-level climate impact compared with synthetics.
- The authors, journal and year of the Woolmark-cited biodegradation study.
- Any sustainability certification for Peregrine’s wool.
Frequently asked questions
Is merino wool better than polyester? It depends on what you measure. Wool is a natural fibre expected to break down more readily, while polyester is plastic that persists. Wool’s farming footprint is higher on some indexes. The strongest factor you control is how long you keep the garment.
What does “mulesing-free” mean? It means the brand says the wool comes from sheep that were not mulesed. Ask which standard or certificate backs the claim.
Does merino wool shed microplastics? Wool is a natural fibre, so it is not a plastic. Every fabric sheds some fibres, but researchers are still studying the types and amounts, so I would not treat any single claim as final.
Is it worth paying more for merino? If you will wear it for years and look after it, often yes. If it ends up in a drawer after one season, no fibre is sustainable.
What has been your experience reading merino labels, and which claim do you wish brands would explain better?
Sources
- Darn Tough, What Is the Responsible Wool Standard? (brand blog, own claims)
- Sheep Inc, Why is wool’s environmental impact badly rated on the Higg Index? (brand FAQ, own claims)
- REI, Microfibers: What We Know So Far (2017, updated 2019)
- Woolmark, Wool and microplastics (industry body, claims not independently checked)
- Rapha, Wool care guide (brand guidance)
- TheIndustry.fashion, Peregrine MD Tom Glover on 225 years of making in England (interview, 9 Dec 2021)
