Compostable, biodegradable, plant-based: greenwashing or progress?

Somewhere a coffee cup is printed with a leaf, the word “plant-based” and a soothing shade of beige. It is telling you a story: this one is different, this one goes back to nature. Sometimes that story is true. Much more often it is true only if a very specific, very hot machine is involved, and nobody tells you whether one exists near you.

Bioplastics aren’t a scam, exactly. They’re a set of real materials wrapped in marketing that blurs three different promises into one feel-good vibe. Here’s how to pull them apart.

Three words, three different promises

The European Commission, not usually a source of snark, warns that these terms “may be misleading.” Its definitions are the cleanest place to start:

• Bio-based (or “plant-based”) describes what the plastic is made from: fully or partially biological resources rather than fossil fuels. The Commission adds that bio-based plastics are “not necessarily biodegradable or compostable.”
• Biodegradable describes what can happen at the end: the material breaks down through microbes, but only under certain conditions. It says nothing on its own about where, or how fast.
• Compostable is a subset of biodegradable: plastics that typically decompose in industrial composting facilities, and first need to be collected.

These overlap in confusing ways. A biodegradable plastic can be made from oil. A plant-based plastic can be chemically identical to the normal stuff: bio-PE and bio-PET, both among the materials in a 2020 study of bioplastic products, are polyethylene and PET made from plants instead of petroleum. They behave like the plastic in any other bag or bottle. They don’t rot. “Plant-based” tells you about the farm, not the landfill.

It’s also a small market making a big noise. The Commission estimated in 2022 that these plastics were 1% of global plastic production capacity, a bit over 2 million tonnes a year. For the basics on resin codes, “recyclable” and other labels, see our guide to what plastic labels really mean.

“Compostable” usually means “in a machine you don’t own”

The most common compostable plastic is PLA (polylactic acid), made from fermented plant sugars and moulded into clear cups, cutlery and “eco” takeaway boxes. It is certified compostable, and in the right place it does break down. The right place is an industrial facility. The Commission notes industrial composting often needs 55–60°C with high humidity, and states plainly that meeting industrial standards “does not imply decomposition also under home composting.”

Outside that machine, PLA is just plastic. US researchers put PLA textiles in flowing seawater and found they did not degrade for more than 428 days, behaving like conventional polypropylene and PET. Cotton and wood-based cellulose fibres in the same test broke down completely in about 35 days. The authors’ verdict is blunt: calling compostable plastics “biodegradable” is misleading because it implies the material breaks down in the environment.

So a PLA cup in a park, a river or your general rubbish is a plastic cup. A PLA cup in your recycling bin is worse: a contaminant. The Commission warns that compostable and biodegradable plastics put in the wrong stream contaminate recycled materials.

The biodegradable bag that kept on carrying

The classic experiment came from the University of Plymouth. Imogen Napper and Richard Thompson took carrier bags sold in UK shops (biodegradable, oxo-biodegradable, compostable and ordinary polyethylene) and left them in open air, buried in soil and submerged in the sea for three years.

Their paper found that none of the bags could be relied on to deteriorate substantially in all three environments. Everything fell to fragments in open air within nine months; that isn’t the same as disappearing, it’s how plastic becomes microplastic. The compostable bag vanished from the marine test rig within three months, but was still present in soil after 27 months, though too weak to hold weight without tearing.

The headline result is in the university’s press release: the biodegradable, oxo-biodegradable and conventional bags all “remained functional as carrier bags” after more than three years in soil or seawater. Napper said: “After three years, I was really amazed that any of the bags could still hold a load of shopping. For a biodegradable bag to be able to do that was the most surprising.”

This was one study of one set of products, and better materials exist. But it punctured the core marketing idea: that “biodegradable” means litter that cleans itself up. The EU has since gone further on the worst offender. It has banned products made from oxo-degradable plastic, ordinary plastic with additives that make it crumble faster into smaller plastic.

Home composting: the backyard test

What about items labelled “home compostable,” designed for the heap at the end of the garden? University College London ran a large real-world test, the Big Compost Experiment. Between 2019 and 2021, 9,701 people in the UK took part, and 1,648 composted packaging at home.

Results were not kind:

• Across 1,307 item results, 55% of items were still clearly visible when people finished composting.
• For items carrying the TÜV “OK compost HOME” certification, 60% were still clearly visible, 12% were in small pieces and 28% could not be found.
• People struggled with the labels. In a random sample of 50 photos of tested items, 46% had no compostable certification at all and 14% were certified only for industrial composting, despite instructions to test home-compostable items.

The authors concluded that home composting is not an effective way to deal with compostable packaging in the UK. Caveats: participants were self-selected enthusiasts, conditions weren’t controlled and results were self-reported. But a sample of keen composters is about the best-case scenario. If they couldn’t make it work, the average shopper with a cold, neglected heap won’t either.

The paper also notes a less visible problem: compostable plastics are incompatible with most anaerobic digestion plants, the system many UK councils use for food waste, and are often removed as contaminants.

“Plant-based” isn’t the same as “chemically cleaner”

A plastic is a polymer plus a cocktail of additives, processing aids and unintended by-products. Changing the feedstock doesn’t automatically change the cocktail.

In the 2020 study, researchers extracted chemicals from 43 bio-based or biodegradable products, mostly food-contact items. 67% of the extracts were toxic to cells in vitro, 42% caused oxidative stress and 23% blocked male hormone activity. 80% contained more than 1,000 chemical signals. Cellulose- and starch-based products tended to be the most toxic, and the authors judged the materials “similarly toxic” to conventional plastics.

This was a lab study on cells, not on people, and it doesn’t show anyone is harmed by a compostable fork. What it does show is that “natural” marketing tells you nothing about chemical safety. That fits our wider point about plastic chemicals in the kitchen: what leaches matters as much as what the base material is.

Newer work points the same way, on thin evidence:

• In a 2026 study, chemicals leached from a starch-PBAT biodegradable mulch film delayed the development of midge larvae at the highest concentrations, while conventional polyethylene mulch had no effect. The authors stress the effects were limited and only at high doses.
• A 2026 review of studies on swallowed bioplastic particles, mostly PLA tested in cells and mice, found signs of inflammation, oxidative stress and gut microbiome changes, while noting how few studies exist.

The fair summary: biodegradable plastics have not been shown to be more dangerous than ordinary plastic, and they haven’t been shown to be safer either. Particles that break down eventually still exist as particles in the meantime.

When compostable genuinely helps

Now the part the cynics skip. Compostable plastic does a real job when three things line up: the item is mixed up with food anyway, there’s an industrial composter that accepts it, and people know which bin it goes in.

The best case is the food-waste caddy liner. Conventional plastic bags are a contamination headache at compost sites: even after operators pull them out, fragments remain in the waste. The Commission calls industrially compostable bags for collecting food waste “a beneficial application”, and says that in Italy and Spain they led to less pollution in food waste and more food waste captured. It also warns that not every region supports them, because they need suitable composting processes. (Paper liners or no liner at all are alternatives some councils prefer, and we found no controlled study comparing liner types.)

When conditions are right, the materials do break down. In a full-scale French windrow trial at an industrial composting site, certified compostable packaging mixed with household food waste lost 98% of its mass in four months, with no harm detected to compost quality. A 2026 follow-up measured leftover particles and found 98.4% of PLA and 92.6% of PBAT had biodegraded. A thick PHBV coffee capsule managed only 49.9%, a reminder that format matters as much as polymer. The first was funded through a packaging research chair at AgroParisTech’s foundation, and both list authors at that chair, so weigh accordingly.

The EU has now written this logic into law. Its packaging regulation says that by 12 February 2028, tea and coffee bags, soft single-serve pods and the sticky labels on fruit must be industrially compostable, because these things end up in food waste anyway. Countries with the right collection and treatment can also require compostable lightweight carrier bags. Everything else made of biodegradable plastic must be designed for recycling instead. That’s a narrow, sensible list, a long way from “compostable everything.”

Labels matter even here. In a 2025 UK trial with 120 households, clearer labels and prompts about which bin to use increased the amount of compostable packaging put in the food and garden waste bin. The authors call for standardised labels. That’s needed, because right now the labelling is the weakest link.

The rules: who is cracking down

United States: the FTC’s 2012 guides

The Federal Trade Commission’s Green Guides say a “degradable” claim with no qualification is deceptive if the item won’t completely decompose within one year after customary disposal. Landfills, incinerators and recycling plants don’t provide those conditions, which rules out most “biodegradable” claims on everyday trash. “Compostable” claims must be qualified if the item can’t be composted at home, or if composting facilities aren’t available to a substantial majority of buyers.

The guides are guidance, not law, and date from 2012. The FTC asked for comments on updating them in December 2022; nearly four years later, we found no revised version.

California: banned words and beige bags

California is stricter. Its Public Resources Code, tightened by AB 1201 in 2021, bans selling products labelled “biodegradable,” “degradable” or “decomposable”, or any product that implies it will break down in a landfill or the environment. It specifically names green, beige or brown tinting on non-compostable plastic bags as an implied claim. Brown-washing, literally.

“Compostable” products must meet the ASTM standard or, for “home compostable,” hold OK compost HOME certification. They must also have total organic fluorine (a marker for PFAS “forever chemicals”) below 100 parts per million, and be labelled so they’re easy to tell apart from non-compostable items.

AB 1201’s toughest requirement, that compostable products be acceptable inputs for certified organic farming, was meant to start on 1 January 2026. Compostable plastics are mostly synthetic polymers, which that rule doesn’t currently allow. CalRecycle granted a two-year extension that expires on 30 June 2027. Watch that date.

SB 343, California’s separate law on “recyclable” claims and the chasing arrows, is a different fight. A federal court blocked its enforcement in July 2026 while a lawsuit by food producers proceeds.

European Union: generic claims banned from September 2026

The EU’s Empowering Consumers directive applies from 27 September 2026. It bans generic environmental claims a company can’t back with recognised excellent environmental performance or spell out clearly on the same label. The directive’s own examples of generic claims include “biodegradable” and “biobased.” An unqualified “biodegradable” on a coffee cup should now be on its way out in EU shops. The Commission’s 2022 framework sets the standard to aim for: a biodegradable label should state which environment the item biodegrades in and how long it takes, in weeks, months or years.

The tougher follow-up, the Green Claims Directive, which would have required claims to be checked before they reached the shelf, has stalled. In June 2025 the Commission said it intended to withdraw it as part of its push to cut red tape, and negotiations with Parliament and member states were called off. We found no sign of it being revived as of October 2026. So the EU has banned vague claims, but not yet built the system to check the specific ones.

So: greenwashing or progress?

Both, depending on the claim.

• “Biodegradable” on its own is close to meaningless, and California and the EU now treat it as a red flag. Plymouth’s report of a “biodegradable” bag still carrying shopping after three years in the soil is the whole argument.
• “Plant-based” or “bio-based” is a feedstock claim. It may cut fossil fuel use; it says nothing about pollution or chemical safety.
• “Compostable” is a real property, but only useful if your local system collects it. Without that, it’s rubbish with a nicer story.
• “Home compostable” is the most honest-sounding label and, on current UK evidence, the least reliable in practice.

The progress is real but narrow: tea bags, fruit stickers and caddy liners going into a working food-waste system. The greenwashing is everything else: compostable cups for towns without composters, leafy beige packaging, and “plant-based” bottles that are plain PET.

What you can actually do

Ranked roughly by how strong the evidence is:

1. Reduce and reuse first. Swapping one single-use item for another single-use item, even a compostable one, doesn’t fix the throwaway habit. The Commission’s own guidance says these plastics should be used when it is not possible to reduce, reuse or recycle. A refillable cup beats a PLA cup every time.
2. Never litter “biodegradable” anything. The Plymouth bags and the 428-day PLA seawater test are clear: in nature, these materials behave like plastic.
3. Check what your council actually collects. If it takes compostable packaging in the food or garden waste bin, use it. If it doesn’t, or uses anaerobic digestion that removes compostable plastic, industrially compostable items go in general waste, not recycling and not your heap.
4. Use compostable caddy liners only if your council asks for them. Some want certified compostable liners, some want paper, some want none. Follow the local rule; it’s set by the plant that receives the waste.
5. Be sceptical of “home compostable” packaging. If you try it, expect it to take much longer than food scraps, and pick out what’s left before spreading the compost.
6. Don’t buy “plant-based” for health reasons. The cell studies show bioplastics carry chemical mixtures as complex as conventional plastic. For food, glass, stainless steel and ceramics are the materials with the best record.
7. Report vague claims. In the EU, unqualified “biodegradable” and “eco-friendly” claims now fall foul of consumer law; in California, “biodegradable” on a product is banned. Regulators act on complaints. Name the brand.

Where the evidence is weak: we don’t have good long-term data on what compostable plastic fragments do in soils outside of industrial compost, controlled comparisons of liner types for food-waste collection, or any human health evidence for bioplastics specifically. For what is known about plastic particles in the body, see our explainer on microplastics inside you.