Why no fibre is truly sustainable or unsustainable

Sustainable material choice comes down to weighing manufacturing, wear and care, and afterlife costs against what a material is actually being used for.

Walk into any conversation about sustainable fashion and you will likely hear the same shorthand: cotton is natural, so it is good; polyester is synthetic, so it is bad. Wool is renewable, viscose is chemical-heavy, recycled fibres are always the safer choice. These labels are comforting because they make decisions simple. They are also, more often than not, wrong.

The truth about material sustainability is less tidy than a checklist of approved and banned fibres. It sits in the details of how a material is made, how it behaves once it is in someone's wardrobe, and what happens to it long after it has been worn out. Understanding those details, rather than reaching for a label, is what separates a genuinely pragmatic approach to material selection from a marketing one.

No fibre is good or bad, only well or poorly applied

In practice, that framing does not hold up. Every material carries trade-offs, and the real question is not whether a fibre is sustainable in the abstract, but whether it is the right choice for a specific application. To make that judgement properly, three types of cost need to be considered together.

The manufacturing cost covers the energy, water, land and chemical inputs required to produce or extract the raw material and turn it into usable fibre and fabric. Every fibre has a production footprint, whether that is the land, water and pesticides needed to grow cotton, the energy-intensive polymerisation of petroleum-based synthetics, or the chemical processing used to convert wood pulp into viscose. Life cycle assessment, the standard method for evaluating a product's environmental impact from raw material extraction through to disposal, treats this production stage as just one checkpoint among several, since the biggest environmental burdens can just as easily show up later in the value chain, during use or disposal.

The wear and care cost covers everything that happens once the material is in use, including how it is washed, dried and maintained. This is where synthetic fibres in particular carry a cost that is often overlooked at the point of purchase: microplastic shedding during washing. Research has shown that shedding varies enormously depending on fibre type and fabric construction. Polyester fleece has been found to shed far more fibres than plain woven polyester, averaging around 7,360 fibres per square metre per litre in a single wash compared with roughly 87 fibres for standard polyester fabric, and in another study focused on acrylic knitwear, a single six-kilogram wash load was estimated to release over 700,000 fibres into the wastewater. Natural fibres are not free of a wear and care cost either. They may require more frequent washing, more energy-intensive drying, or specific detergents, and this ongoing cost can, over a garment's lifetime, outweigh the impact of its production.

The afterlife cost covers what happens once the item is no longer wanted, including the practicality and impact of recycling, composting, incinerating or landfilling it. Natural fibres generally biodegrade, but this only holds where the fabric is not blended with synthetics or treated with finishes that block decomposition. Synthetic fibres do not biodegrade in any meaningful timeframe, but they can, in principle, be mechanically or chemically recycled, provided the material stream is not contaminated by fibre blends, which remain one of the hardest problems in textile recycling today.

That is why no fibre has a fixed sustainability score. Wool, cotton, polyester, nylon and every other material has genuine strengths, and the task of a designer is to identify where those strengths can be put to proper use rather than dismissing or defaulting to a material based on reputation alone. When selecting materials for a design, all three costs need to be weighed against the intended application: how the item will be used, how often it will be washed, how long it is expected to last, and how it will eventually be disposed of. Only once those factors are compared against each other can a properly informed decision be made about whether a material is the best possible choice for that specific purpose.

The better question

This does not make design harder, only more honest: instead of asking whether a fibre is sustainable, the better question is what it is costing, and where.

Applying that question changes how a choice gets made. Take a base layer worn for high-intensity exercise, washed after nearly every use and expected to last only a handful of seasons. A synthetic fabric brings a wear and care cost that is hard to ignore, given how much it sheds in the wash, but a cotton equivalent would demand more water and land at the manufacturing stage while managing moisture far less effectively during actual use. A shirt intended for occasional wear and infrequent washing tells a different story: here, a natural fibre's higher production footprint may be offset by a much lower wear and care cost over its lifetime. Neither fibre is disqualified by the comparison. What changes is which cost carries the most weight for that specific use.

The same logic applies at the other end of a garment's life. A single-fibre polyester garment, once worn out, has a viable path to being recycled, whether mechanically into shorter-fibre applications or, increasingly, chemically back into virgin-equivalent PET. A poly-cotton blend in the same category is a harder problem altogether, since separating the two fibres before either can be processed remains one of the most persistent obstacles in textile recycling. Afterlife cost, in other words, can outweigh whatever advantage a blend offered in performance or feel.

Laid out side by side against the intended use of a garment, manufacturing, wear and care, and afterlife costs tend to make the right material obvious, or at least narrow the field to a short, defensible list.

No fibre will ever be perfect. Designing well simply means keeping its trade-offs in view when making the choice, and being honest about which of the three costs a specific design can least afford to ignore.