Why your “100% wool” sweater might contain plastic

Wool has long been positioned as one of fashion’s most natural, renewable fibres: warm, breathable, biodegradable, and capable of lasting decades. But in today’s textile system, even garments labelled “100% wool” may not be as pure as they appear.

The culprit is not the fibre itself, but what happens to it after shearing.

The hidden processing behind modern wool

Most commercially available wool today is treated to improve convenience, specifically, to make it machine washable and resistant to shrinking. This process is known as superwash treatment.

To achieve washability, wool fibres undergo chemical modification:

• The fibre’s natural scales are altered or removed

• The surface is coated with a synthetic polymer resin

• The result is smoother fibres that resist felting

These coatings can include plastic-based compounds designed to stop fibres from locking together in water. In effect, the wool still originates from sheep, but the finished textile behaves partly like a synthetic material.

What superwash treatment changes

Untreated wool has remarkable natural properties:

• Temperature regulation

• Breathability

• Moisture-wicking

• Odour resistance

• Biodegradability

However, heavy processing can diminish these qualities. Some treatments also rely on chlorine-based processes before applying the polymer coating, which has raised environmental concerns due to chemical waste streams. From a circular-fashion perspective, polymer-coated fibres are harder to recycle and may shed microscopic particles as the coating degrades.

Why this matters for sustainability

Fashion’s shift toward natural fibres is real; consumers are increasingly seeking alternatives to fossil-fuel-based synthetics. Yet if natural fibres are heavily treated, the environmental benefits can be partially undermined.

Superwash wool, for example:

• Requires additional chemical processing

• May behave less like a natural fibre in end-of-life scenarios

• Can reduce biodegradability depending on treatment

• May contribute to microplastic pollution via coatings

Convenience has quietly reshaped what “natural” means in modern textiles.

Certifications: What they do (and don’t) guarantee

Navigating wool labels is confusing because certifications address different stages of production.

Woolmark

Verifies fibre authenticity, that the product contains real wool.
Does not guarantee chemical-free processing.

OEKO-TEX® Standard 100

Tests finished products for harmful substances within safety limits.
It focuses on toxicity thresholds, not whether synthetic coatings are present.

Responsible Wool Standard (RWS)

Ensures animal welfare and land stewardship, with supply-chain traceability.
It does not restrict superwash processing.

“Organic Wool”

Refers to how sheep are raised, not how fibres are finished.
Organic wool can still be chemically treated.

Global Organic Textile Standard (GOTS)

Currently, the strongest indicator of both organic fibre sourcing and restricted processing methods.

GOTS certification applies to the entire product and prohibits many conventional shrink-resistant treatments, including chlorine-based superwash processes. If you want the closest thing to truly natural wool in a finished garment, look for GOTS-certified products, not just organic fibre claims.

How to identify more natural wool garments

While no system is perfect, you can reduce the likelihood of heavily processed wool by:

1.Look for full-product certifications

• GOTS (strongest overall indicator)

• RWS + processing transparency
  Brands openly discussing finishing methods
  
  

2.Check care labels
Machine-washable wool often signals superwash treatment.

3.Ask brands direct questions
Responsible companies should be able to explain processing methods.

4.Prioritise durability over convenience
Hand-wash-only wool often indicates minimal treatment.

The return of “real” wool

Encouragingly, interest in untreated and low-impact wool is growing. Designers focused on circular fashion, regenerative agriculture, and slow production are revisiting traditional wool processing methods that preserve the fibre’s natural integrity.

Natural wool does require more care, but it also offers longevity that fast fashion cannot replicate.

The issue is not wool itself, but a system optimised for speed, uniformity, and low maintenance. True sustainability asks a deeper question:

Do we want clothing that behaves like disposable synthetics, or garments designed to age, repair, and endure?

Choosing fewer, better-made pieces from transparent supply chains remains one of the most powerful actions consumers can take.

Because when natural fibres are allowed to remain natural, they become part of a regenerative system rather than a linear one.