Yes, wool is generally considered biodegradable. It is a natural protein fiber, so under the right conditions microorganisms can break it down. How quickly that happens depends on the conditions and on what the garment is made of.
Short answer
Pure wool will break down over time when it is in contact with moisture, warmth and microbes, such as in soil. Blended or treated wool may take longer, and a garment sitting dry in a landfill is unlikely to decompose quickly.
Why wool breaks down
Wool is made of keratin, a protein also found in hair and nails. Fungi and bacteria produce enzymes that digest this protein. The Woolmark industry body notes that clean, dry wool fibers resist degradation, which is part of why woolen items are durable in everyday use. Once wool is warm, moist and buried in soil, it becomes much easier for microbes to break down.
How long does wool take to decompose?
There is no single figure. Woolmark, which represents the wool industry, reports that 100% Merino wool fabric biodegraded by around 95% after 15 weeks of burial in soil in testing, while stating that the rate varies with soil, climate and wool characteristics. That is a favorable result from an industry source, and real-world conditions are less controlled. Commonly quoted ranges run from months to a few years, but treat those as rough estimates.
What slows it down
- Blends. Wool mixed with polyester, nylon or acrylic is only partly biodegradable, and the synthetic portion will persist.
- Dyes and finishes. Some chemical treatments, such as certain dyes, flame retardants or shrink-resistant finishes, may affect how fabric breaks down or what it releases.
- Trims. Zips, plastic buttons and elastic do not biodegrade and are best removed first.
- Conditions. Dry, cold or oxygen-poor landfill conditions slow decomposition.
Wool compared with synthetics
Synthetic fibers such as polyester and acrylic are made from petroleum-based materials and break down extremely slowly, if at all, in normal conditions. Natural fibers generally return to the soil more readily. That said, end-of-life is only one part of a fabric’s footprint. Production, water use, land use and how long a garment lasts also matter. See our article on caring for polyester for the synthetic side.
What fabrics are 100% biodegradable?
Untreated natural fibers such as cotton, linen, hemp, silk and wool are generally biodegradable. The word “100%” is difficult to guarantee, since dyes, finishes, blends and thread can all change the picture. Regenerated cellulose fibers such as viscose and lyocell are often considered biodegradable too. For a broader look at plant-based options, see vegan clothing fabrics.
Is wool environmentally friendly?
It is mixed, and reasonable people disagree. Wool is renewable and biodegradable and tends to be long lasting, but sheep farming has environmental impacts, including land use and methane emissions, and animal welfare is a concern for some buyers. Choosing secondhand wool, wearing items for many years and caring for them well reduces their impact. If you avoid animal products, wool is not an option, as explained in our vegan fabrics guide.
What is the unhealthiest fabric to wear?
There is no definitive answer. Individual reactions differ: some people find wool itchy, and others react to dyes or finishes. If you have skin sensitivities, speak with a health professional, and washing new clothes before wearing them is a common precaution.
Caring for wool so it lasts
Keeping wool in use is one of the best things you can do for the environment. In general:
- Wash only when needed, using cool water and a gentle or wool-specific detergent, or hand wash.
- Avoid heat and heavy agitation, which can cause felting and shrinkage.
- Dry flat.
- Store clean, and protect from moths.
- Mend holes and moth damage early.
More general advice is in our fabric care guide.
When it is time to let go
Donate or resell wearable items, reuse worn wool for patchwork, stuffing or crafts, and check whether local textile recycling accepts it. As a last resort, wool scraps can be composted if they are pure wool, cut small and free of synthetic trims. Garment-sewing considerations are discussed in is sewing your own clothes sustainable.