The two words get used as though they mean the same thing. They don’t, and the gap between them decides what happens to a bag after it goes in the bin.
Here is the short version. “Biodegradable” means a material can eventually be broken down by living organisms. It sets no deadline and names no conditions. “Compostable” means the material has been tested against a written standard and will break down, disintegrate, and leave no toxic residue inside a fixed window. One is a description anyone can print on a bag. The other is a certification someone has to earn.
Where the Confusion Starts
Part of the problem is marketing. Part of it is that “biodegradable” sounds more precise than it is.
Compare it to the word “edible.” Technically, a great many things are edible. That tells you nothing about whether you would want to eat them, or what happens if you do. “Biodegradable” works the same way. Microorganisms can break the material down eventually. The useful questions come after: how long, under what conditions, and into what?
Why the Distinction Has Commercial Consequences
For a business buying packaging, the difference shows up in three places.
Compliance. Vague environmental claims are being legislated against. The EU’s Green Claims Directive and a growing list of national single-use plastic bans both push buyers toward claims that can be documented rather than asserted. A supplier who can hand you a certificate is a different kind of supplier from one who can only hand you a brochure.
Customer complaints. A compostable liner that fails in a customer’s home compost bin, or a “biodegradable” bag that a municipal facility rejects, becomes someone’s problem. Usually yours.
Cost of getting it wrong. Landfill disposal fees, contamination penalties at composting facilities, and replacement orders all land on the buyer when a claim turns out to be thinner than advertised.
None of this is abstract. It is the difference between a claim and a test report.
What Biodegradable Bags Actually Are
Biodegradable bags break down through the action of microorganisms — bacteria, fungi, and the like. That much is straightforward. Conventional plastic bags may sit in a landfill for centuries; biodegradable ones are designed to break down sooner.
They can be made from a wide range of materials. Bio-based plastics, modified conventional plastics, and blends all get sold under the same word. Some manufacturers add chemical additives to accelerate breakdown. That breadth is exactly why the term is unreliable: it covers materials with almost nothing in common.
What “biodegradable” does not promise
Two things get lost in the marketing.
Speed and conditions aren’t specified. The term is largely unregulated. A bag can carry the label while taking decades to break down, or while needing industrial heat it will never encounter in a landfill. An apple core rots in a garden in weeks. Put the same apple core in a low-oxygen landfill and it can still be recognisable years later. Many biodegradable bags follow that second path. They never get the oxygen or the microbial activity the process requires.
The end products aren’t guaranteed. Landfills are built to contain waste, not to decompose it. When organic material does break down anaerobically, it produces methane, a greenhouse gas far more potent than carbon dioxide over the short term. And some biodegradable plastics don’t fully mineralise at all. They fragment into microplastic particles, which then move into soil, water, and eventually the food chain.
Biodegradable bags can outperform conventional plastic in specific settings. Landfill is not one of them.
What Compostable Bags Are
Compostable is a different category of claim. These bags are not just designed to disappear; they are designed to return nutrients to soil, and to do it on a schedule somebody can verify.
What they are made of
Certified compostable film is usually built from three components.
- PLA (polylactic acid) is the rigid one. It comes from plant starch, typically corn or sugarcane, and gives the film its strength and stiffness.
- PBAT (polybutylene adipate-co-terephthalate) is the flexible one. It supplies softness, stretch, and resistance to tearing.
- Corn starch, or thermoplastic starch is the renewable filler. It lowers cost and speeds up degradation.
The ratio between them is the engineering decision, and it determines how the finished bag has to be disposed of. It is worth looking at two real grades side by side, because the numbers tell a more honest story than any adjective.
| Feature | XH-918 (home compostable) | SH-133 (industrial compostable) |
|---|---|---|
| Base blend | Corn starch + PLA + PBAT | PLA + PBAT |
| Density | 1.2 g/cm³ | 1.2 g/cm³ |
| Melting point | 140–145 °C | 155–165 °C |
| Melt flow index | ≤10 g/10 min | ≤15 g/10 min |
| Tensile strength | ≥12 MPa | ≥20 MPa |
| Elongation at break | ≥400% | ≥300% |
| Flexural modulus | ≥100 MPa | ≥500 MPa |
Read the last three rows together. The home-compostable grade is less stiff — a flexural modulus of 100 MPa against 500 — but it stretches considerably further, with elongation at break above 400% versus 300%. That is not a defect. It is the trade-off. More starch and less PLA gives a softer film that will break down in a backyard bin at lower temperatures. The same formulation choice that makes home composting possible also makes the film more pliable and less rigid.
The melting points support the same reading: 140–145 °C for the starch-heavy grade, 155–165 °C for the PLA-heavy one.
A buyer who understands that trade-off asks different questions. Not “is it compostable?” but “compostable where, and which property am I trading away to get it?”
Both grades are documented in full on their own pages: XH-918, the corn starch based resin and SH-133, the PLA/PBAT resin. For how the two disposal routes compare in practice, see home vs industrial composting.
The standards behind the claim
“Compostable” has a definition, and it is a strict one.
- EN 13432 is the European standard for compostable packaging. We break its requirements down in our EN 13432 guide.
- ASTM D6400 is its United States counterpart, covering plastics and products processed in municipal and industrial facilities.
- AS 4736 and AS 5810 cover industrial and home composting in Australia and New Zealand. For the difference between the two, see AS 4736 vs AS 5810.
To pass, a material has to do three things.
Biodegrade. Break down into carbon dioxide, water, inorganic compounds, and biomass, typically at least 90% within 180 days, at a rate comparable to natural materials.
Disintegrate. Physically break into fragments small enough to be invisible in finished compost, within a defined period — usually 90 to 180 days.
Pass ecotoxicity testing. Leave no heavy metals or harmful residues behind that would contaminate the compost.
Certification is what separates the two categories in practice. Logos worth looking for include TÜV AUSTRIA OK Compost and OK Compost HOME, DIN CERTCO, and BPI. A bag carrying one of these has been tested by a third party, not assessed by its own manufacturer. We explain how the schemes differ in our compostable certification guide.
One further trap: oxo-degradable bags. These are conventional plastic with a metal-salt additive that makes them fragment into microplastics. They meet no compostability standard and are restricted or banned in several regions, including the EU. The word on the bag may look similar. The material is not.
Why the compostable route pays off environmentally
The environmental case rests on where the material ends up.
Compostable bags are designed for composting systems — an industrial facility, or a home bin where the grade is certified for it. They enter a process that can actually complete.
They are typically made from renewable plant material, which absorbed carbon dioxide while it grew. When the bag breaks down, that carbon returns to the soil rather than adding fossil carbon to the atmosphere.
And because certified grades are tested for ecotoxicity, they can be composted alongside food waste instead of contaminating it. That is what makes them useful in food waste collection: the bag and its contents go in together.
Biodegradable vs. Compostable, Side by Side
| Feature | Biodegradable | Compostable |
|---|---|---|
| Definition | Breaks down eventually; no fixed timeframe | Breaks down into compost within a defined timeframe |
| Conditions | Unspecified; may require light, air or heat that never arrives | Defined composting conditions: heat, humidity, microbial activity |
| Timeframe | Unregulated — months, years or decades | Regulated — typically within 180 days industrially, up to about a year at home |
| End products | CO2, water, and potentially microplastics | Humus, CO2, water; no toxins |
| Certification | ASTM D6691, ISO 14855, ISO 23517, ISO 19679, ISO 23832 | ASTM D6400, EN 13432, OK Compost / OK Compost HOME, AS 4736, AS 5810 |
| Disposal | General waste | Industrial or home compost |
| Materials | Anywhere from bio-based plastics to modified conventional plastics | Plant-based blends such as corn starch, PLA and PBAT |
What This Means for a Business
Three arguments carry weight with buyers and with procurement teams.
Certified claims survive scrutiny. In a market where every supplier claims to be green, a certificate is the part that can be checked. It also protects you if a customer or a regulator asks for evidence.
It fits existing waste streams. Compostable liners work with food waste collection because the bag and the food scraps are processed together. That removes a sorting step and reduces contamination.
It closes a loop rather than delaying a problem. Organic waste becomes compost instead of landfill volume. That is a materially different outcome from a bag that simply breaks into smaller pieces somewhere out of sight.
Where Compostable Bags Are Used
The applications where certified compostable film earns its cost tend to share one feature: the bag and organic waste are collected together.
Food waste collection. Household caddies, restaurant kitchens, and commercial food preparation all produce wet organic waste. A compostable liner goes into the bin with the contents, which removes the messy step of emptying and rinsing a bin and keeps the waste stream clean enough to be accepted.
Retail and grocery. Compostable shopping and produce bags give stores a bag that can be reused at home and then composted. Our compostable produce bags and custom compostable grocery bags are specified for this.
Takeaway and delivery. Food service packaging that can be composted alongside food scraps avoids the fork-and-container sorting problem that contaminates most recycling streams. Our custom compostable take-out bags are made for this.
Agriculture and film. Where the film rather than the bag is the product, the same materials logic applies. See our compostable masterbatch for the additive side of those formulations.
Two Objections Worth Answering
“Compostable costs more.” It usually does, per unit. The comparison that matters is the total cost: avoided landfill tax and disposal fees, less contamination, and a packaging claim you can put in front of a customer without hedging. Unit price is one line in that calculation, not the whole of it.
“There’s no composting facility near me.” True in many places, and worth being honest about. Two things follow. Home-compostable grades exist precisely for customers without access to industrial facilities — that is what the OK Compost HOME and AS 5810 marks certify. And collection infrastructure follows demand; it is being built in response to volume, not in advance of it.
How to Check a Compostable Claim
Five questions, in order.
- Which logo is on it? BPI, OK Compost, OK Compost HOME, DIN CERTCO, or AS 4736 / AS 5810. A plain “biodegradable” label answers nothing.
- What does the certificate say? Ask for the biodegradation figure and the timeframe — for example, 90% within 180 days.
- Where is it meant to be composted? Industrial and home grades are not interchangeable. Check which one you are buying.
- Can the supplier produce third-party test data? Ecotoxicity and heavy metal results are part of the standard, so the reports exist. A supplier who cannot produce them has not been through the process.
- Is it oxo-degradable? If so, it is not compostable, whatever the packaging says.
FAQS
Is biodegradable the same as compostable?
No. Biodegradable means a material can eventually break down, with no guaranteed timeframe or conditions. Compostable means it meets a written standard such as EN 13432 or ASTM D6400 and breaks down into non-toxic compost within a defined window.
How long do compostable bags take to break down?
Certified compostable bags typically biodegrade within 90–180 days in an industrial facility. Home-compostable grades take longer, often close to a year, depending on temperature and moisture. We break the variables down in how long compostable bags take to decompose.
Which certifications should I look for?
ASTM D6400 or BPI in North America; EN 13432, TÜV OK Compost or DIN CERTCO in Europe; AS 4736 for industrial and AS 5810 for home composting in Australia.
Are oxo-degradable bags compostable?
No. They are conventional plastic with an additive that makes it fragment into microplastics. They meet no compostability standard and are restricted or banned in several regions, including the EU.
Will a compostable bag break down in my home compost bin?
Only if it carries a home-composting certification such as OK Compost HOME or AS 5810. Industrial grades need the higher temperatures of a commercial facility.
Why is a home-compostable film softer than an industrial one?
Home-compostable grades use more starch and less PLA, so they break down at lower temperatures. The same change makes the film more flexible and less rigid — for example, elongation at break above 400% and a flexural modulus around 100 MPa, against 300% and 500 MPa for a typical industrial grade.