Biodegradable vs Compostable Plastic Bags: What Actually Certifies
A supermarket buyer in Melbourne sent us a bag last October, sealed in a zip pouch with a printed logo we had never seen. The label said “100% biodegradable & compostable”. Two weeks later our lab partner sent back a photo of the film after 90 days in a compost reactor: broken into flakes, but the flakes were still there, and total carbon converted to CO2 was under 40%. It was a starch-blended polyethylene with a pro-oxidant additive. Biodegradable in the loose sense. Not compostable by any standard that exists.
That pouch is why this category is a minefield. The vocabulary is barely regulated; the certificates are. Compare what the papers say.
Four certificates, four very different promises
| Standard / scheme | Who issues it | What it proves | Time and conditions | Bags it covers | ||
|---|---|---|---|---|---|---|
| EN 13432 | Accredited EU labs, certifier issues | Industrial compostability: 90% disintegration by mass within 12 weeks at 58 ± 2 °C, 90% biodegradation (CO2 evolution) within 6 months, ecotoxicity pass, heavy metals under limits (zinc 150 mg/kg, copper 50) | Industrial only; not a home box | Yes | ||
| ASTM D6400 | US labs, then BPI certification | Same thresholds as EN 13432, US test methods; the BPI logo is the market mark, and BPI now screens for PFAS | Industrial composting | Yes | ||
| OK Compost HOME | TÜV Austria | Disintegration and biodegradation at ambient backyard temperature, ~25 °C, up to 12 months with weaker inoculum activity | Home compost bin; thick film rarely passes | Only thin starch-based films realistically | ||
| Oxo-degradable | No legitimate scheme | Nothing. | A pro-oxidant additive in PE/PP makes film fragment, not biodegrade; residue is microplastic | N/A | Banned for many uses in the EU |
The EU banned oxo-degradable plastics under Directive (EU) 2019/904 from 3 July 2021. Article 5 restricts them on the EU market outright, and the Commission’s review found no evidence they biodegrade in landfill, soil or sea. If a supplier offers “oxo-biodegradable” carrier bags for an EU retail account, there is no compliance path.
What this means for a bag you want to actually sell
Retail and grocery is where risk concentrates: the bag is in the customer’s hand, photographed, carrying your client’s logo. Three things line up or the sale falls apart.
The certificate must name the product, not the company. A document for “starch-based film, 20 µm” does not cover your 30 µm printed bag on a different resin lot. Buyers accept PDFs saying only “our products are certified”; that is worthless in a customs dispute.
The claim must match the disposal route. EN 13432 does not make a bag home-compostable, and “compostable at home” is a false claim in several EU member states. A HOME-certified thin film can also be too slow for a facility’s 12-week residence time, and some composters reject it as contamination.
The printing and adhesive must be inside the certification. Water-based inks are standard for compliant film; solvent inks and some lamination adhesives carry PFAS or push heavy metals past the EN 13432 limits. This is the failure we see most when a buyer’s design was certified only as plain film.
How we verify a sample, in practice
When a buyer sends us a bag to match, we run this before quoting. Most fail at step two.
- Certificate number and issuing body — BPI, TÜV Austria, DIN CERTCO. We check the issuer’s public register, not the supplier’s website.
- Scope check — product description, film thickness range, and whether printing is included.
- Date check — an expired certificate means the last batch was not covered.
- Resin identity — PBAT/PLA/starch blend, with a data sheet naming the grade. If the supplier won’t name the resin, walk away.
- PFAS declaration — batch-linked, not a generic letter. US state laws (Maine, Minnesota, Washington) and EU restrictions make this live for food-contact bags.
- A disintegration test — 8 weeks in a 58 °C reactor on a 200 g sample. It catches pro-oxidant film immediately.
Then ask for the batch code on the bag and a certificate linked to that lot. Our paper carry bags fall under a different scheme, but the audit discipline is identical, and our paperwork is listed on the compostable certification standards page.
Where bagasse and paper bags fit
Careful here. Kraft paper bags are compostable in the same industrial sense, and many pass EN 13432, but one with a PE window or plastic handle is a mixed material and fails. We make kraft bags with paper handles for that reason. Choosing between compostable film and paper for a retail client comes down to load strength, moisture, and whether the local waste stream accepts film. Our guide to home vs industrial composting covers what happens to each.
Straight talk on cost: a certified carrier bag runs roughly 2 to 4 times a conventional PE bag at the same size. HOME-certified film costs more again, because fewer resin grades qualify. On 10,000 bags that gap is real money, and it does not disappear at volume.
FAQ
Are biodegradable bags the same as compostable bags?
No. Biodegradable carries no time limit and, in most jurisdictions, no test method. Compostable means a specific standard, usually EN 13432 or ASTM D6400, was met and certified by a third party. A bag can be labelled biodegradable and still leave plastic fragments a year later.
Are oxo-degradable bags banned in the EU?
Yes. Article 5 of Directive (EU) 2019/904 bans oxo-degradable plastic on the EU market from 3 July 2021. The ban covers bags and other single-use items made with pro-oxidant additives. Retailers who import them carry liability, not just the factory.
Can a compostable bag go in a home compost bin?
Only with OK Compost HOME or equivalent. EN 13432 and ASTM D6400 bags need sustained 55–60 °C, which a backyard pile never reaches. Film at 40 µm and above is likeliest to fail.
How long does a certified compostable bag take to break down?
Under EN 13432, 90% must disintegrate into pieces under 2 mm within 12 weeks and 90% must biodegrade within 6 months. In a real facility the bag is usually gone in 8 to 14 weeks.
What document should I ask a supplier for?
The certificate, with scope covering your exact product, thickness and print, a current expiry date, the issuer’s registration number, the resin data sheet, and a batch-linked PFAS declaration.
Are compostable bags more expensive?
Yes, typically 2–4 times conventional PE. Buy them for compliance and market access, not unit price.
If you have a bag on your desk and cannot tell what it is, send us the sample and the certificate. We’ll say so straight, even if the answer is that we can’t make it. Request a quote with dimensions, load target and country of sale.
