Superwash Wool: How it’s made, environmental tradeoffs, and why responsibly-made wool often still beats acrylic

In terms of sustainability, nothing beats untreated (non-superwash) wool. Unfortunately, untreated wool can be difficult to dye, and even more difficult to care for. It must be hand washed in cold water, laid flat to dry, and handed with extreme care. It's prone to felting, takes significantly more water to dye and rinse, and doesn't take color as vibrantly as treated wool. It has microscopic barbs on it that interlock when rubbed together, which is what causes the shrinkage that wool is notorious for. For some people (I'm one of them), those microscopic barbs also cause skin irritation, which can lead many people to incorrectly believe they are allergic to wool. It's just not practical for most people to use untreated wool, so textile scientists created an alternative option, called "superwash" wool. This is the only type of wool that I dye, and even though it's not as sustainable a untreated wool, it's still a fantastic option that's better for the earth than synthetic fibers, like acrylic yarn.

This page explains the common industrial and research methods used to make wool “superwash” (machine-washable, non-felting) and weighs the environmental pros and cons of each. It also addresses a frequent claim — that superwash wool is “just plastic” — and shows why, when you examine supply chains and treatment methods, wool frequently retains lifecycle advantages over acrylic and many other synthetic alternatives. This page does a deep dive into the scientific processes used, so you can skip all of that and just read the summary if you don't want to go into too much detail. 

Why wool felts — and what “superwash” must change

Wool fibers have overlapping surface cuticle scales. Heat, moisture and mechanical agitation make those scales interlock — that’s felting and shrinkage. Superwash methods either (A) blunt or remove those scales, or (B) coat the fiber with a smooth film so the scales can’t catch. High-magnification SEM images are the clearest way to show this.

Main superwash methods — how they work, pros & cons

A. Chlorine oxidation + polymer resin (classic “Chlorine–Hercosett”)

How it works: Controlled oxidation with chlorine (hypochlorite or gaseous chlorine) partially etches or loosens cuticle scales; a cationic polyamide-epichlorohydrin resin such as Hercosett 125 is applied and fixed to form a smooth protective film on the fiber. This combination produces exceptionally durable machine-washability. 

Pros: Highly effective, inexpensive at industrial scale, durable through many washes.

Cons: Chlorination can produce AOX (adsorbable organic halogens) in effluent; epichlorohydrin chemistry and the final PAE resin are petrochemical and largely non-biodegradable. AOX formation and regulatory wastewater limits are the primary environmental concerns for this route. 

B. Chlorine variants & AOX-reduction engineering

Some mills use improved chlorine reactors, scrubbing and effluent treatment to reduce uncontrolled AOX. These reduce risk but do not remove the fundamental dependence on chlorine chemistry and resin finishes. 

C. AOX-free oxidative methods (ozone, peroxide) + alternative binders

Using ozone or hydrogen peroxide instead of chlorine can avoid AOX formation; pairing these oxidants with non-halogenated binders yields AOX-free superwash processes in pilot and industrial trials. Performance often approaches the classic route when the binder is optimized. 

D. Enzyme (protease) based anti-felting finishing

Proteases selectively digest or soften the cuticle layer, reducing felting tendency. Enzymes are biodegradable and lower-toxicity chemistry; modern enzyme protocols are improving durability and reducing fiber damage when carefully controlled. However, enzymes alone often require additional fixation or mild binders for long-term durability.

E. Plasma / low-pressure & atmospheric plasma surface modification

Plasma treatments physically oxidize and modify the fiber surface (removing lipids, creating hydrophilic groups, changing topology). Plasma can act as an AOX-free pre-treatment and deliver durable anti-felting when combined with appropriate binders. The EU LIFE SUPERWOOL project developed plasma-based approaches explicitly to replace chlorine/Hercosett. 

F. Alternative polymer coatings (silicones, polyacrylates, graft polymers)

Mills sometimes use silicone emulsions or acrylic/methacrylate-based films instead of PAE resins; these can avoid halogen chemistry but are still synthetic polymers (raising biodegradability and microplastic concerns). 

Environmental evidence: key facts to weigh

1. AOX risk from chlorine + resin is well documented. This is the single most-cited environmental issue with the classic process — regulatory limits and wastewater controls focus on AOX measurement. 
2. Hercosett-type resins are polyamide-epichlorohydrin (PAE) polymers. They form a crosslinked, cationic film; epichlorohydrin is reactive and its use and residues are regulated for health/safety reasons. 
3. Acrylic (polyacrylonitrile) is fossil-derived and not biodegradable. Acrylic fiber manufacture is petrochemical- and energy-intensive; acrylic garments are a known source of synthetic microfibers when laundered. 
4. Enzyme and plasma routes materially reduce hazardous chemistry. Enzyme and plasma pre-treatment options remove AOX formation risk and are increasingly shown to produce durable anti-felting when combined with non-halogenated binders. 
5. There is no single universal LCA that settles wool vs acrylic for every scenario. Lifecycle results are highly sensitive to boundaries (cradle-to-gate vs cradle-to-grave), local energy mix, wastewater treatment, and product lifetime. Because wool is renewable and often longer-lasting, it frequently performs better — but uncontrolled chlorine effluent can make some impact categories worse. 

Why responsibly-finished superwash wool is still better than acrylic:

• Renewable & biodegradable base material: Wool is a natural, renewable fiber that biodegrades in appropriate conditions — acrylic does not. This is a foundational material advantage. 
• Longer usable life: Wool garments often last longer (thermal performance, pilling/wear characteristics), and a longer lifetime reduces environmental footprint per use. LCAs that include lifetime frequently favor wool. 
• Microfiber context: . Acrylic is a well-documented source of synthetic microfibers. Polymer coatings on wool could theoretically release fragments if they degrade, but the data on resin-film shedding are limited; acrylic’s laundering microfiber problem is a proven impact.
• We can eventually eliminate the worst chemical problems: AOX risk from chlorine can be removed by selecting AOX-free processes (plasma, enzyme, ozone + non-halogenated binders) as they become more readily available, or by sourcing mills with strict effluent controls. When those are used, wool keeps its material advantage and avoids the main chemical downside.