Most flexible compostable bags are not made from a single material.
They are commonly produced from blends of compostable polymers such as PBAT and PLA, often combined with starch or thermoplastic starch, plus small amounts of processing aids, colourants or printing inks where required.
The exact formulation varies according to the bag’s application, thickness, strength, flexibility, colour, printing and intended composting system.
One important point is often misunderstood:
Compostable does not necessarily mean 100% plant-based.
PLA is typically bio-based, while commercially used PBAT is often fossil-derived. A material can therefore be compostable without being entirely plant-based.
Last reviewed: October 19, 2026
Quick Answer: What Are Compostable Bags Made Of?
Typical flexible compostable bags may contain:
| Material | Main Role in Compostable Bag Film |
|---|---|
| PBAT | Flexibility, toughness and film performance |
| PLA | Rigidity, strength and bio-based content |
| Starch / thermoplastic starch | Renewable content and formulation adjustment |
| Processing additives | Help with film processing and product performance |
| Colour masterbatch / pigments | Provide the required bag colour |
| Printing inks | Used when logos, instructions or branding are printed |
There is no single universal formula for every compostable bag.
Different manufacturers, applications and certified product configurations may use different material ratios and components.
What Are Compostable Bags
A compostable bag is a bag designed so that its materials can biodegrade and disintegrate under specified composting conditions.
That does not mean the bag will quickly disappear anywhere in the environment.
Commercial composting, industrial composting and home composting are different environments, and products intended for these systems may be assessed against different standards and certification schemes.
For a more detailed explanation of the term itself, see: What Is Compostable? Definition, Standards & Meaning Explained
This page focuses specifically on a different question:
What materials are compostable bags actually made from?
What Is Compostable Plastic Made Of?
The term compostable plastic does not refer to one specific polymer.
Instead, it can describe plastic materials or blends designed to meet defined compostability requirements.
For flexible bags, some of the most commonly encountered materials are PBAT, PLA and starch-based materials.
Their properties are different, which is why they are often blended instead of being used individually.
PBAT — Polybutylene Adipate Terephthalate
PBAT is a flexible polyester widely used in compostable film applications.
Its main value in bag production is flexibility and toughness.
Flexible bags need to withstand stretching, handling, sealing and, depending on the application, puncture or tear forces. PBAT can help provide the soft and flexible characteristics required for blown-film products.
A common misunderstanding is that PBAT is a plant-based plastic.
That is not necessarily correct.
Commercial PBAT is commonly produced from fossil-derived feedstocks, although the origin of a polymer and its biodegradation behaviour are separate questions.
In other words:
Bio-based describes where the carbon comes from. Compostable describes how a material behaves under specified composting conditions.
They do not mean the same thing.
PBAT is therefore useful for understanding why a compostable bag can contain a compostable polymer without being made entirely from plants.
PLA — Polylactic Acid
PLA, or polylactic acid, is a bio-based polyester commonly produced from fermented plant-derived sugars.
Feedstocks may include crops such as corn, sugarcane or other sugar-producing plants, depending on the resin manufacturer and production process.
PLA is generally more rigid than PBAT.
This can contribute structure and strength to a material blend, but PLA by itself is usually too stiff or brittle for many thin flexible bag applications.
This is one reason PLA and more flexible polymers are often combined in compostable films.
However, being made from PLA does not automatically mean a finished bag is certified compostable, nor does the use of plant-derived feedstock automatically make a product suitable for home composting.
The finished formulation and product still matter.
Starch and Thermoplastic Starch
Starch is another renewable material used in some compostable plastic formulations.
Common sources include corn, potato, cassava and other starch-producing crops.
Natural starch cannot simply replace conventional plastic film on its own. For plastic processing, starch may be modified or converted into thermoplastic starch, often abbreviated as TPS, and combined with other polymers.
Depending on the formulation, starch-based components may contribute to:
- renewable material content;
- processing characteristics;
- mechanical properties;
- cost and formulation balance.
The amount of starch used can vary significantly between material systems.
Therefore, it is not accurate to assume that all compostable bags are simply “corn-starch bags.”
Some contain starch. Others may contain very little, and some compostable polymer systems may use different materials altogether.
Are There Additives in Compostable Bags?
Yes. A compostable bag formulation may contain more than its main polymers.
Small amounts of other constituents may be used to support manufacturing or the required finished-product properties.
These can include processing aids, colourants, pigments, masterbatch and other formulation components.
Printed bags also contain printing inks.
The important distinction is that the presence of an additive cannot be evaluated independently from the finished formulation.
A claim such as:
“PLA + PBAT + starch = certified compostable”
is too simplistic.
Compostability assessment may need to consider the complete product, including relevant polymers, additives, colourants, inks, thickness and construction.tified compostable bags are tested to ensure that approved additives do not interfere with composting performance.
Do Compostable Bags Contain Plastic?
Yes — many compostable bags are technically plastic films.
The word “plastic” describes a broad category of polymer materials. It does not automatically mean that every plastic has the same raw-material source or the same end-of-life behaviour.
For example, conventional shopping or trash bags are commonly made from polyethylene such as HDPE or LDPE.
Many flexible compostable bags instead use compostable polymer blends that may contain materials such as PBAT and PLA.
So:
Compostable plastic is still plastic, but it is not necessarily the same type of plastic as conventional polyethylene bags.
This distinction is useful because terms such as “plastic-free,” “plant-based” and “compostable” should not be treated as interchangeable claims.
Are Compostable Bags 100% Plant-Based?
Not necessarily.
This is one of the most important material distinctions to understand.
Some components, such as PLA and starch, can be produced from renewable plant feedstocks.
Other compostable polymers may be partly or primarily fossil-derived.
Therefore, a bag can be:
bio-based and compostable; partly bio-based and compostable; or compostable while containing fossil-derived polymer components.
Whether a material biodegrades under a specified composting environment depends primarily on its chemical structure and the applicable test conditions—not simply on whether the original feedstock came from a plant or from fossil resources.
That is why “plant-based” should not be used as a substitute for “compostable.”
Why Are Compostable Bags Made From Material Blends?
A thin flexible bag has to perform several jobs at the same time.
It needs enough strength to carry its contents, enough flexibility to avoid tearing too easily, suitable sealing performance during production, and sufficient stability during its intended shelf life and use.
One polymer may perform well in one area but poorly in another.
PLA, for example, can contribute rigidity but is relatively stiff for flexible film applications.
PBAT provides substantially greater flexibility.
Starch-based components introduce another set of properties.
By combining different materials, formulators can adjust the balance between:
strength, flexibility, tear behaviour, sealing, film processing, thickness, colour, printing and intended end-of-life performance.
There is therefore no “best” PLA/PBAT/starch ratio for every bag.
The appropriate formulation depends on the finished product.
For a deeper discussion of how PLA and PBAT work together in flexible films, see:
Why Use PLA PBAT Compostable Bags
For procurement and material-selection questions, see:
Compostable Bag Materials: The Ultimate B2B Buyer’s Guide
How Are Compostable Bags Made?
The production process is similar in several respects to conventional flexible-film bag manufacturing, but the processing conditions and material formulation are selected for the compostable resin system being used.
The main stages typically include material preparation and extrusion, blown-film production, printing where required, and bag converting.
During blown-film extrusion, the polymer material is melted and extruded into a continuous tubular film.
After cooling, the film can be printed and then converted into the required bag structure.
Depending on the product, converting may include sealing, cutting, perforation, folding and rolling.
The finished bags are then checked against the required specification, such as dimensions, thickness, sealing quality, printing and packaging configuration.
This explains why the material alone does not determine the quality of a compostable bag.
Film formulation, extrusion control and bag converting are all part of the final product performance.
How Do Compostable Bags Work?
Compostable polymers are designed so that microorganisms can break down the material under the conditions for which it was designed and assessed.
Composting involves a combination of factors including microorganisms, moisture, oxygen, temperature and time.
The required conditions are not identical in every composting system.
Commercial or industrial composting systems generally operate under managed conditions, while home composting environments usually operate at lower and more variable temperatures.
For that reason, a product intended for industrial composting should not automatically be described as home compostable.
Likewise, “compostable” does not mean that a bag is designed to rapidly disappear in landfill, soil, waterways or the open environment.
Does a PLA/PBAT Material Blend Prove That a Bag Is Compostable?
No.
Knowing the polymer names is useful for understanding the material, but it does not by itself establish a certification claim for a finished product.
Two bags can both be described as PLA/PBAT-based while differing in:
thickness, polymer ratios, additives, colourants, printing inks, construction and intended composting environment.
Certification programs evaluate products or materials according to defined schemes and requirements.
Therefore, the safer rule for buyers is:
Do not infer finished-product certification from the words PLA, PBAT, starch, biodegradable or compostable resin alone.
Certification applicability should be confirmed against the applicable current certificate and final finished-product specification.
For ORIZON certification references, certified product scopes and verification information, see: ORIZON Evidence & Verification Center
What Are Compostable Produce Bags Made Of?
Compostable produce bags are commonly made from flexible compostable polymer formulations similar to those used in other thin-film compostable bags.
Depending on the required specification, a formulation may contain PBAT, PLA, starch-based components and other permitted constituents.
However, produce bags often have different requirements from heavy-duty waste bags.
They may prioritize characteristics such as low film thickness, softness, transparency or translucency, easy opening and roll dispensing.
The exact formulation therefore depends on the required finished product rather than simply the words “produce bag.”
What Are Compostable Food Waste Bags Made Of?
Food-waste and organic-waste liners are also commonly produced from flexible compostable polymer blends.
PBAT may contribute flexibility and toughness, while PLA, starch-based materials and other components can be used to adjust the overall film properties.
Again, there is no single formula shared by all food-waste bags.
Size, thickness, load requirements, moisture exposure, storage conditions and the intended composting system can all affect the required material design.
Compostable Bags vs Biodegradable Bags
“Biodegradable” and “compostable” should not automatically be treated as synonyms.
Biodegradation is a broad biological process.
A compostable product is expected to meet defined requirements under specified composting conditions.
Therefore, asking:
“What are biodegradable bags made of?”
does not lead to one universal material answer.
Products marketed as biodegradable can use many different material systems, and the term alone does not establish that a bag is suitable for a particular composting system.
For a detailed comparison, see:
Difference Between Biodegradable and Compostable Bags
FAQ
What are compost bags made of?
Flexible compost bags are commonly made from blends of compostable polymers such as PBAT and PLA, sometimes combined with starch or thermoplastic starch and smaller amounts of additives, colourants or inks. The exact formulation depends on the product.
What are compostable bags made from?
There is no single raw material used for every compostable bag. Common components include PBAT, PLA and starch-based materials.
What is compostable plastic made of?
Compostable plastic may be made from one or more polymers designed for biodegradation under specified composting conditions. Flexible bag formulations commonly use PBAT, PLA and starch-based components.
Do compostable bags contain plastic?
Many do. PBAT and PLA are polymers and are commonly classified as bioplastics or compostable plastics. “Compostable” does not mean “plastic-free.”
Is PBAT plant-based?
Commercial PBAT is commonly fossil-derived. Its ability to biodegrade under specified conditions is related to its chemical structure rather than simply whether its feedstock is plant-based.
Is PLA plant-based?
PLA is generally a bio-based polymer produced from fermented sugars derived from renewable feedstocks such as sugarcane, corn or other sugar-producing crops.
Are compostable bags made from corn starch?
Some compostable bag formulations contain corn starch or thermoplastic starch, but not all compostable bags are primarily made from corn starch.
Do compostable bags contain additives?
They can. Additives, processing aids, pigments, masterbatch and printing inks may form part of the finished formulation depending on the product.
Are all PLA and PBAT bags compostable?
No certification conclusion should be made from polymer names alone. Compostability depends on the formulation, finished product, applicable standard or certification scheme, and intended composting environment.
Do compostable bags leave microplastics?
This cannot be determined simply by reading the ingredient list. Compostability standards and certification schemes assess defined biodegradation, disintegration and compost-quality requirements. For a specific product, the appropriate certification and intended composting conditions should be checked.
Conclusion
So, what are compostable bags made of?
For flexible bag applications, the answer is usually a material blend rather than one single ingredient.
PBAT commonly contributes flexibility.
PLA can contribute rigidity and bio-based content.
Starch-based materials may provide renewable content and help adjust the formulation.
Additional constituents may be used for processing, colour and printing.
Most importantly:
“Bio-based,” “plant-based,” “biodegradable” and “compostable” do not mean exactly the same thing.
The material list helps explain how a bag is made, but it does not by itself prove the certification status of the finished product.
- For buyers evaluating formulations, thickness, film performance or OEM specifications, continue with: Compostable Bag Materials: The Ultimate B2B Buyer’s Guide
- For a detailed explanation of PLA and PBAT in flexible bag production: Why Use PLA PBAT Compostable Bags
- For current certification references and applicable product scopes: ORIZON Evidence & Verification Center
