Compostable bags are primarily made from plant-based bioplastics such as PLA (polylactic acid), PBAT, and starch- or cellulose-based materials. These materials are designed to fully break down into water, carbon dioxide, and biomass under controlled industrial composting conditions.
As a manufacturer with 16 years of experience in producing compostable bags, this guide will explain: what compostable bags are made of, how these materials work, how compostable bags differ from biodegradable plastic bags, how to identify certified compostable bags, and how to dispose of them correctly after use. I’ll keep it practical and clear, and hope it will be helpful to you.
What Are Compostable Bags
A compostable bag is a bag that can fully break down into water, carbon dioxide, and organic matter under specific composting conditions.
This matters.
Compostable does not mean “breaks down anywhere.” It usually means industrial composting, where heat, oxygen, and moisture are carefully controlled.
To be called compostable, a bag must meet recognized standards, such as:
- ASTM D6400 (United States)
- EN 13432 (Europe)
- AS 4736 / AS 5810 (Australia)
These standards define how fast and how completely the material must break down.
What Are Compostable Bags Made of
Most compostable bags are made from a blend of materials. No single material works well on its own.
PLA (Polylactic Acid)
PLA is one of the main ingredients. It is made from plant sugars, usually from corn or sugarcane. PLA gives the bag structure and strength. However, PLA is stiff. On its own, it cracks easily.
PLA also needs high heat to break down properly, which is why industrial composting is important.
Source: Wikipedia – Polylactic acid External link: https://en.wikipedia.org/wiki/Polylactic_acid
Are There Any Additives in the Compostable Bags?
In addition to the main ingredients, compostable bags often contain additives such as antioxidants, plasticizers, and other additives to make the bags more durable and easier to process.
Are these additives completely safe and will not affect the composting process? This is a question worth considering. Certified compostable bags are tested to ensure that approved additives do not interfere with composting performance.
PBAT (Polybutylene Adipate Terephthalate)
PBAT solves a problem PLA cannot. PBAT is flexible. It allows the bag to stretch instead of tearing.
In simple terms:
- PLA provides strength
- PBAT provides flexibility
- Without PBAT, most compostable bags would not work in real life.
PBAT is designed to biodegrade fully under composting conditions, even though it is not plant-based.
Source: Wikipedia – PBAT External link: https://en.wikipedia.org/wiki/Polybutylene_adipate_terephthalate
Starch-Based and Cellulose Materials
Some compostable bags also include:
- corn starch
- potato starch
- cellulose or wood pulp
These materials help with structure and composting performance. They are renewable and widely used in certified formulations.
Manufacturer insight
From my experience as a compostable bag manufacturer, the balance between PLA and PBAT matters more than the ingredient list itself.
Too much PLA makes bags brittle. Too much PBAT weakens structure. Certification exists because these balances are hard to get right.
Understanding these materials also helps explain what is compostable waste, since only materials that fully break down under composting conditions belong in compostable waste systems.
How Do Compostable Bags Break Down?
Compostable bags do not disappear on their own.
They need:
- temperatures around 55–60°C (130–140°F)
- oxygen
- moisture
- active microorganisms
This environment is found in industrial composting facilities, not in landfills and not always in home compost piles.
When these conditions are met, the materials are broken down by microbes and turned into basic organic components.
Are There Additives in Compostable Bags?
Yes, sometimes.
Compostable bags may contain small amounts of additives to:
- improve processing
- control aging
- maintain strength during use
Certified compostable bags are tested to ensure these additives do not interfere with composting.
This is why certification matters more than marketing claims.
Do Compostable Bags Leave Microplastics?
This is a common concern.
Under proper industrial composting conditions, certified compostable bags are designed to break down completely, without leaving plastic residue.
However, problems can occur when:
- composting temperatures are too low
- bags end up in landfills
- bags enter the natural environment
In those cases, breakdown may be incomplete. The key factor is disposal, not just material.
Compostable vs Biodegradable Plastic Bags
These two terms are often confused.
They are not the same.
| Feature | Biodegradable Bags | Compostable Bags |
|---|---|---|
| Main materials | Plastic with additives | PLA, PBAT, starch |
| Breakdown conditions | Unclear or slow | Defined composting systems |
| Residue | Possible microplastics | No toxic residue |
| Certification | Often none | ASTM, EN, AS standards |
| End result | Partial breakdown | Water, CO₂, biomass |
Biodegradable does not automatically mean compostable.
For more information on biodegradable vs compostable, see this article：Difference between biodegradable and compostable bags
How to Identify Truly Compostable Bags
The safest way is to look for certification.
Reliable standards include:
- BPI certification (U.S.)
- ASTM D6400
- EN 13432
- AS 4736 / AS 5810 (Australia)
Certified products are listed in official databases.
You can verify certified products using official directories:
- BPI directory : https://bpiworld.org/
- TÜV / DIN CERTCO registration: https://m.dincertco.tuv.com/registrations/60152087?locale=en
(If you want, you can also checke Our BPI identification number (10529118) can be verified on the official BPI directory can be verified here : 10529118.)
How to Use Compostable Bags
A few simple rules help avoid problems:
- Use compostable bags only for organic waste
- Do not mix them with regular plastic
- Store them away from heat and sunlight
- Do not reuse them for long-term storage
Compostable bags are designed for short use cycles.
How to Dispose of Used Compostable Bags
Best options depend on your local system.
Best choice:
- Industrial composting or food waste collection programs
Acceptable in some areas:
- Community composting facilities
Not recommended:
- Landfills
- Recycling bins
When compostable bags go to the wrong place, their benefits are lost.
FAQ
Are Biodegradable Bags Compostable
Only if they are certified to compostable standards such as ASTM D6400 or EN 13432.
Do compostable bags really break down completely?
Yes, under proper industrial composting conditions.
Can compostable bags be composted at home?
Sometimes, but home compost systems often lack the heat needed for full breakdown.
Conclusion
Compostable bags are not magic. They are engineered products. They are made from PLA, PBAT, and plant-based materials, designed to work in specific composting systems.
When used and disposed of correctly, they reduce long-term plastic pollution. When used incorrectly, they behave like any other waste.
Understanding what compostable bags are made of helps you make better choices—and avoid false claims.
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