What "Bio-Based" Actually Measures (And What It Doesn't)
by KWAN SHING
Published on
August 21, 2026
Bio-based content is a measurement, not a virtue. It is the ratio of a product’s new organic carbon to its total organic carbon, determined by a standard test method. It describes where the carbon atoms came from, and it says nothing at all about how the material behaves at end of life.
What is bio-based content, precisely?
The definition used by the United States Department of Agriculture’s BioPreferred programme is unusually clean for this field: biobased content is a ratio of a product’s new organic carbon to total organic carbon, as measured by a standard test method (ASTM D6866).1
New organic carbon comes from plant and forestry materials. Old organic carbon comes from petroleum, which has been out of the carbon cycle for millions of years. The test can tell them apart because living matter contains a small, predictable proportion of a radioactive carbon isotope that fossil feedstock has long since lost. Measure the isotope ratio, and you get a percentage that is genuinely difficult to fake.
So a material described as 40 % bio-based is telling you that roughly four in ten of its organic carbon atoms entered the material from a plant rather than a barrel. That is a real, physical, laboratory-verifiable statement. It is also a narrower statement than most buyers assume.
Why bio-based does not mean biodegradable
The European Commission is blunt on this point: bio-based plastics are not necessarily biodegradable or compostable.2
The two properties are decided at different stages. Feedstock origin decides whether a material counts as bio-based. Molecular structure decides whether microbes can break it down. A polymer built from plant-derived sugars can be chemically identical to its fossil-derived twin, in which case it will persist in the environment for exactly as long. Conversely, some readily biodegradable polymers are made from fossil feedstock.
The Commission also warns that the umbrella term bioplastics is often used to describe very different materials, and that the terms bio-based, biodegradable and compostable may be misleading.2 When those three words appear together in one sentence of supplier marketing, treat it as a prompt to ask which one is actually being claimed and on what evidence.
The percentage without a denominator problem
Here is where most bio-based claims quietly lose their meaning. The test measures organic carbon. It does not measure the whole product.
Consider a coated fabric. If the coating is 50 % bio-based by carbon, and the coating is 30 % of the laminate by weight, and the backing textile is conventional polyester, then a headline claim of 50 % bio-based describes a slice of a slice. Every part of that is technically true and the overall impression is wrong.
The Commission has flagged exactly this gap, noting there is no clarity regarding the part of a plastic product that is entirely or partly derived from biomass, and that no EU sustainability criteria currently apply to bio-based plastics.2 Until that changes, the burden sits with the buyer. Ask three things: what percentage, measured on what component, as a share of what total.
What the number tells you about actual impact
Very little on its own, and that is not a criticism of the metric — it is simply outside its scope.
Bio-based content says nothing about how the crop was grown, how much land or water it took, whether it displaced food production, how the biomass was processed, how much energy the conversion used, or what happens to the material after use. A material can be highly bio-based and still carry a heavy footprint if the feedstock is irrigation-intensive and the conversion is energy-hungry.
Used properly, the number answers one question well: how much of this material’s carbon has been pulled out of fossil supply chains. That is genuinely useful, and it belongs alongside other evidence rather than standing in for it. Treat it as one line in a specification, not as a summary judgement about the material.
How to check a bio-based claim before you specify
A workable check runs in four steps.
- Ask for the test report, not the adjective. A bio-based percentage should trace to a laboratory result under a recognised radiocarbon method. If nobody can produce one, the figure came from a calculation or from marketing.
- Establish the denominator. Which component was tested, and what share of the finished article does that component represent by weight.
- Separate the three claims. Bio-based, biodegradable and compostable each need their own evidence. Do not let one certificate carry all three words.
- Check whether third-party certification exists. Some programmes verify the content independently — a certified product under the USDA scheme, for instance, has achieved third-party verification of biobased content before it may display the label.1
None of this requires technical expertise on your side. It requires asking for the denominator, which is the question that most claims are not built to survive.
Frequently asked questions
How is bio-based content measured?
By radiocarbon analysis under a standard test method such as ASTM D6866, which compares the amount of new organic carbon from plant sources with the total organic carbon in the sample.
Is a bio-based material always better than a fossil-based one?
Not automatically. The metric only describes carbon origin. Land use, water use, processing energy and end-of-life behaviour all sit outside it and have to be assessed separately.
Can a bio-based plastic be composted?
Only if it has been separately tested and certified as compostable. Bio-based plastics are not necessarily biodegradable or compostable, because feedstock origin and molecular structure are independent properties.
What percentage counts as bio-based?
There is no universal threshold, and that is precisely why the denominator matters. Ask what was tested, what percentage it returned, and what share of the finished product that tested component represents.
Related materials
Send us a bio-based claim and we will help you read it. Swatches, sampling and certification documentation are available through SUS Materials on request.
References
1. USDA BioPreferred Program, About BioPreferred — definition of biobased content as a ratio of new to total organic carbon measured by ASTM D6866, and third-party verification of certified products. biopreferred.gov
2. European Commission, Biobased, biodegradable and compostable plastics — biobased plastics are not necessarily biodegradable or compostable; lack of clarity on which part of a product derives from biomass; no EU sustainability criteria currently apply. ec.europa.eu