Is Merino Wool Sustainable? An Honest Assessment

Merino base layer top shown from the front

It depends entirely on what you are measuring. Wool is renewable, biodegradable and durable. It also has a high carbon footprint per kilogram, driven overwhelmingly by methane from the sheep. Anyone selling merino as straightforwardly the sustainable choice is skipping the second half, and anyone dismissing it on carbon alone is skipping the first. Here is what the research supports about the wool garments we sell.

Start with the uncomfortable number

Published life cycle assessments put virgin wool somewhere in the range of roughly 10 to over 100 kg CO₂ equivalent per kilogram of fibre. That is a very wide band, and the width is itself informative — it reflects genuine differences in farming systems and, more importantly, in how emissions are divided between wool and the meat from the same animal.

The dominant contributor is enteric methane, the by-product of ruminant digestion, along with nitrous oxide from manure. Analyses commonly attribute upward of three quarters of wool’s climate impact to these two sources. Nothing about the spinning, dyeing or shipping of a garment moves the number as much as the sheep do.

By comparison, polyester’s carbon footprint per kilogram is considerably lower, because it is made from fossil feedstock in an industrial process rather than grown on an animal. On this single metric, synthetic wins clearly.

The other costs people skip

  • Land use. Sheep farming requires extensive grazing land. On non-arable land this can be a reasonable use; where it drives overgrazing it degrades soil, reduces biodiversity and can accelerate erosion.
  • Scouring. Washing raw wool to remove lanolin, dirt and vegetable matter is water- and energy-intensive, and produces heavily contaminated effluent that requires treatment.
  • Chemical treatment. The chlorine-Hercosett process that makes merino machine washable involves chlorine chemistry and effluent management. The convenience of a machine-washable garment has a real cost attached.
  • Dyeing and finishing. Shared with every textile, and not trivial.
  • Animal welfare. A separate concern from environmental impact, and a genuine one. Mulesing practices vary by region and certification.

What wool has going the other way

Biodegradability is the clearest advantage and it is well evidenced. A 2024 study of marine biodegradation found wool — including chlorine-Hercosett treated wool — degraded substantially in seawater, while synthetic fibres showed little or none and polyester showed no apparent degradation. Wool fibres shed in the wash break down; polyester fibres persist as microplastic pollution.

Renewability is the second. Sheep regrow fleece annually on inputs that are largely grass. Polyester depends on extracted fossil feedstock.

The third is the one that matters most in practice and gets discussed least: wool garments are worn more times between washes and tend to last longer. Impact per wear, rather than per kilogram, is the metric that reflects how clothing is actually used — and on that basis a merino garment worn four times per wash for five years compares very differently than the raw fibre figure suggests.

Why per-kilogram comparisons mislead

What actually reduces impact

The evidence points consistently at consumption rather than fibre choice. The largest reductions available to an individual come from buying less, keeping garments longer and washing them less — and those hold regardless of what the garment is made from.

  1. Buy fewer, better garments. Manufacturing dominates the footprint of most clothing. Halving how much you buy beats optimising what you buy.
  2. Keep them in service longer. Repair, and choose blends where durability is the constraint. A garment lasting twice as long halves its impact per wear.
  3. Wash less, and wash cold. This is where merino has a real advantage, because odour resistance makes fewer washes practical rather than merely virtuous.
  4. Skip the tumble dryer. Energy, garment life and airborne fibre release all improve at once.
  5. Buy secondhand where you can. The impact of a garment already made is close to zero at the point of purchase.
  6. Consider recycled wool. Mechanically recycled wool has been assessed at a small fraction of virgin wool’s carbon footprint, since it skips the farming stage entirely.

So should you buy merino?

If it replaces several synthetic garments and you keep it for years, the case is reasonable — you are trading a higher upfront footprint for durability, fewer washes and fibres that do not persist when shed. If it is an addition to an already-full wardrobe, no fibre argument makes it a sustainable purchase.

Buy it because it performs well for how you dress, and reduce impact through how much you buy and how you care for it. That is a defensible position. Merino as an environmental virtue in itself is not one.

Our guide on whether synthetic clothes shed microplastics covers the fibre-persistence evidence in more detail, and how often to wash merino covers the habit that does most of the work. Browse base layers and merino socks if you have decided it suits you.

Related merino guides

Sources

Image: Merino Mart catalogue. Browse base layer tops.