Writing honest sustainability copy is harder than it sounds. The temptation is to stretch the claim — it reads better, it moves more stock, and until recently it was low-risk. That era is ending fast. UK regulators are actively investigating greenwashing, EU rules are tightening, and customers are sharper than they were five years ago. This guide covers what you can and cannot say, with real language we use on copywriting projects at OakFox.

The Regulatory Backdrop (UK and EU)

Two frameworks matter in 2026:

UK — CMA Green Claims Code

The Competition and Markets Authority’s Green Claims Code is the UK’s rulebook. It sets six principles:

Claims must be truthful and accurate
Claims must be clear and unambiguous
Claims must not omit or hide important information
Comparisons must be fair and meaningful
Claims must consider the full life cycle of the product
Claims must be substantiated

The CMA has been opening enforcement cases since 2022. ASOS, Boohoo, Asda, and Unilever have all been subject to investigations. Fines and undertakings are real outcomes.

EU — Green Claims Directive

The EU Green Claims Directive takes effect from 2026. If you trade in the EU, environmental claims must be:

Pre-verified by an accredited body before publication
Evidenced with specific scientific data
Not relying on generic offsets

“Climate neutral”, “eco-friendly”, and “green” as standalone words are on the list of prohibited vague claims.

If you trade in both markets — most UK brands do — assume the stricter EU rules.

What You Cannot Say (Without Substantiation)

Even with good intentions, certain language is now effectively prohibited or extremely risky:

Avoid	Why
”Eco-friendly”	Meaningless without specificity. CMA flagged example.
”Natural”	Legally ambiguous. Arsenic is natural.
”Green” as a standalone descriptor	Too vague under EU Green Claims Directive.
”Carbon neutral” / “Net zero”	Allowed only if the methodology is published and verified.
”Planet-positive” / “Climate-positive”	Scientifically unsubstantiable at the product level.
”100% recyclable”	Only if collection exists at scale in your customer’s area.
”Sustainable” without context	Requires specific, measurable backing.
”Plant-based” applied to plastics	Misleading if less than 30% bio-content.
Green/leaf/globe imagery dominating product ID	Can be misleading even if copy is accurate.

What You Can Say (With Substantiation)

The good news: specific, evidenced, narrow claims are strong. Customers respond to them. Here is the pattern:

Pattern 1 — Specific input claim

Weak: “Made from sustainable cotton.”

Strong: “Woven from GOTS-certified organic cotton, grown and milled in Turkey.”

You have named the certification, the material, the process, and the geography. Everything is checkable. Customers who care can verify. Customers who do not, trust you more because the specifics signal honesty.

Pattern 2 — Specific outcome claim

Weak: “Our packaging is eco-friendly.”

Strong: “Our packaging is 100% FSC-certified cardboard with water-based inks. It is recyclable through standard UK kerbside collection.”

Two certifications cited, one input component named, and the collection route specified — so the recyclability claim does not collapse when a customer tries to recycle it.

Pattern 3 — Honest partial claim

Weak: “Sustainable supply chain.”

Strong: “Our wool comes from farms within 60 miles of the mill. The dyes are Oeko-Tex 100 certified. We do not yet know the footprint of our shipping labels — we are working on it.”

Naming the part you know about and the part you do not is the single biggest credibility move available. Customers trust brands that admit limits far more than brands that claim perfection.

Pattern 4 — Comparison claim

Weak: “Our product is better for the environment.”

Strong: “Compared to our 2022 product, this one uses 34% less virgin plastic by weight. Measured against the same SKU.”

Specify the baseline, specify the metric, specify the like-for-like condition. Claims without a baseline are unfalsifiable and therefore regulatorily risky.

Pattern 5 — Process claim

Weak: “We care about the planet.”

Strong: “We donate 1% of revenue to [named charity], independently verified in our annual report (link).”

Care is not a claim. Money and verified action is a claim.

The Language We Use at OakFox

For our own site, the sustainability language is deliberately cautious:

Deployed to verified renewable-powered hosting on The Green Web Foundation’s registry.

Not “green hosting”. Specific provider, specific verification, specific independent registry. A customer can check the claim in thirty seconds. (For a worked example of which UK hosts pass that test, see our green web hosting UK comparison — or browse our managed green web hosting plans if you want someone to handle the move.)

Static-first architecture minimising energy per visit through smaller page weights and fewer requests.

Not “we care about carbon footprint”. Specific technical decision, specific mechanism, specific measurable outcome.

We do not claim ISO-accredited auditor status. For enterprise carbon accounting or CSRD reporting we refer to specialists.

Naming the limit is more credible than pretending the limit does not exist.

This is the pattern to replicate: every claim should be checkable, specific, and modest about what it does not cover.

A Simple Test

Before publishing any sustainability claim, run it through these four questions:

If a regulator asked me to substantiate this in writing within 14 days, could I?
If a journalist investigated this claim, is there anything in my supply chain that would embarrass me?
If a customer read this claim, then read our full sourcing page, would they feel the two are consistent?
If I am comparing my product to an earlier version or a competitor, is the comparison like-for-like?

If any answer is “no” or “not sure”, either gather the evidence first or rewrite the claim more narrowly.

The Commercial Case

Being careful about sustainability claims is often framed as a marketing compromise. It is the opposite. Specific claims convert better than vague ones because:

Trust compounds. A customer who believes your smaller claim is more likely to believe your next claim.
Specificity is memorable. “34% less virgin plastic” sticks; “better for the environment” does not.
Regulatory investigations destroy brands. The downside of a CMA case is far larger than the upside of a slightly better conversion rate.
Customers tell the difference. Sharp audiences increasingly recognise greenwashing and punish it with disloyalty, bad reviews, and public criticism.

The brands that have come out of the last five years strongest — Patagonia, Allbirds, Ecover, Mother of Pearl — are the ones who erred on the side of specificity. The ones quietly rebranding are the ones who did not.

Common Mistakes I See Every Month

Claiming something the supply chain partner has done. If your cardboard supplier is FSC certified, that does not mean your product is. The claim has to describe a change in your business, not one you inherited.
Using “net zero” loosely. Net zero has a specific scientific definition (SBTi methodology). Most “net zero” claims would not survive a technical review.
Mixing aspirations with achievements in the same sentence. “We use organic cotton and are working toward biodegradable packaging” — the reader assumes both are current.
Relying on offsets. Carbon offsets have fallen significantly in regulatory favour. A sustainability strategy that leans on offsets is a strategy with a short shelf life.
Putting sustainability on the homepage when it is not in the product. If the first thing a customer reads is sustainability copy, the product better deliver. If it does not, the homepage becomes the weakness, not the strength.

If In Doubt

If in doubt about a claim, do one of three things:

Rewrite narrower. Name the specific mechanism and omit the broader claim.
Gather evidence first. Ship the data, then ship the copy.
Drop it. Not every page needs a sustainability line. A product page that does not claim anything is more trustworthy than one that overclaims.

We write copy for sustainability-driven brands as part of our copywriting service — and the first thing we do on every project is audit existing claims for defensibility. If you have sustainability copy on your site or products and want a second read, send us a few lines. We reply within 24 hours.

How to Write Sustainability Claims That Aren't Greenwashing