Whats is PBAT?
PBAT (polybutylene adipate terephthalate) is a fully biodegradable polymer used as the active ingredient in compostable packaging. It is the material responsible for making compostable mailers, bags and films actually break down in compost conditions without leaving microplastics or toxic residues behind.
If you've ever bought a compostable mailer or seen packaging labelled home compostable, PBAT is likely what made that claim possible.
What does PBAT stand for
PBAT stands for polybutylene adipate terephthalate. It is a synthetic biodegradable co-polymer, meaning it is engineered from multiple chemical components to achieve specific properties : in this case, flexibility, strength, and the ability to fully biodegrade when composted.
What is PBAT made from
PBAT is derived partly from petrochemicals (petroleum), which is worth understanding clearly. Unlike conventional plastic, which is also petroleum-derived but engineered to be as durable and permanent as possible, PBAT is engineered at a molecular level to break down when exposed to the right biological conditions.
The presence of butylene adipate groups in its molecular structure is what enables PBAT to biodegrade fully. This is a fundamentally different outcome to conventional plastic, even though both start from similar raw material sources.
Research into fully plant-based alternatives to PBAT is ongoing, and higher bio-based PBAT formulations are being developed , though increasing the plant-based content can affect the rate of compostability.
Why PBAT is used in compostable packaging
PBAT is used because it solves a core problem in compostable packaging: flexibility. Plant-based materials like PLA (polylactic acid) are rigid and brittle on their own. PBAT acts as the flexible, stretchy binding agent that gives compostable mailers their toughness , comparable to the feel and durability of conventional plastic mailers, while still allowing the product to biodegrade.
Without PBAT, compostable mailers would crack, split, or fail in transit. It is what makes the material suitable for real-world ecommerce shipping.
How PBAT, PLA and cornstarch work together
Most compostable mailers, including HeapsGood Ecomailers, are made from a blend of three materials:
PBAT: the flexible, biodegradable co-polymer that provides stretch, toughness and the ability to compost. This is the active ingredient that drives breakdown in compost conditions.
PLA (polylactic acid): a bioplastic derived from plant-based sources such as corn starch. PLA provides rigidity and structure to the blend.
Corn starch: an organic filler derived from corn, contributing to the bio-based content of the material and supporting breakdown.
Together, this blend produces a material that performs like plastic during its useful life but is designed to fully biodegrade when composted.
How quickly does PBAT break down
Under suitable compost conditions, PBAT-based compostable packaging is designed to break down within 180 days in home compost, and within 90 days in commercial or industrial compost conditions.
This aligns with EN 13432, the compostability standard now referenced in Australia, which requires packaging to fully disintegrate within defined timeframes and leave no harmful residues.
PBAT breaks down through the action of naturally occurring microorganisms , including bacteria, fungi and algae, which metabolise the polymer chains. This process does not produce microplastics.
PBAT vs conventional plastic
Conventional plastic is engineered to resist degradation for as long as possible. Even plastics made from recycled content remain plastic-based materials that depend on recycling infrastructure to avoid ending up in landfill or the environment , infrastructure that processes less than 10% of plastic annually in Australia.
PBAT-based materials are engineered for the opposite outcome: complete biological breakdown at end of life. When composted correctly, they do not leave behind microplastic fragments or toxic residues.
The key distinction is not where the raw material comes from, but what happens to the material at end of life. PBAT is designed to return to the natural environment. Conventional plastic is not.
Does PBAT break down in landfill
PBAT will break down in landfill, but like any organic material in an anaerobic (oxygen-free) landfill environment, this process produces methane , a greenhouse gas. Compostable packaging is designed for compost conditions, not landfill.
For the full environmental benefit of PBAT-based packaging, it should be composted , either at home or through a commercial composting facility. Many Australian councils now offer green waste bins that accept certified compostable packaging, though acceptance varies by council.
What certifications confirm PBAT-based packaging is compostable
The certification landscape in Australia for compostable packaging has recently changed. AS 4736 (industrial compostable) and AS 5810 (home compostable) were previously the applicable Australian standards , and you will still see these referenced widely online and on older packaging. However, these standards are no longer applicable for compostable mailers and non-food-contact compostable packaging in Australia.
The standard now referenced for compostable packaging in Australia is EN 13432: a European compostability standard that has become the recognised benchmark.
It is worth understanding what this change means and what it does not mean. The material itself (PBAT, PLA and cornstarch blends) has not changed. It is still fully compostable and will still biodegrade in compost conditions. The change is regulatory, not material. Products that were compostable before this shift are still compostable.
The practical impact of the change is that compostable mailers can no longer be accepted in Australian council green waste bins under the old AS standards. Food-waste-associated compostable products such as bin liners remain accepted because they are directly associated with food waste streams. Compostable mailers, however, have been caught out by the reclassification , not because the material is any different, but because of how the policy has been drawn.
This is a frustrating and arguably short-sighted outcome. Rather than working with composting facilities to develop better sorting and processing solutions, the regulatory change has effectively removed a genuinely compostable product from council green waste streams without addressing the underlying infrastructure problem. The material still biodegrades. The issue is policy, not science.
When evaluating any compostable packaging today, look for EN 13432 certification rather than AS 4736 or AS 5810, and be cautious of products still making green bin claims that are no longer supported under current Australian standards.
Is PBAT safe
Yes. PBAT is designed to leave no toxic residues after composting. Certified compostable products must demonstrate this through testing. Products that pass Australian compostability standards are required to leave behind no harmful substances after biodegradation.
PBAT is used in food-contact applications internationally and is recognised as safe for composting environments.
PBAT and the future of compostable packaging
PBAT is currently the most practical and widely available material for producing flexible compostable packaging at commercial scale. It is not a perfect solution , as its partial petroleum derivation means it is not fully renewable, but it is the most viable option available today for replacing plastic mailers with a product that genuinely biodegrades.
Ongoing research is focused on developing higher bio-based content alternatives and fully plant-derived binding agents. The packaging industry is moving in this direction, and PBAT represents the current best available technology rather than the end state.
Frequently Asked Questions
What is PBAT in compostable packaging?
PBAT (polybutylene adipate terephthalate) is the active biodegradable ingredient in compostable packaging. It provides flexibility and strength while enabling the material to fully break down in compost conditions.
Is PBAT a plastic?
PBAT is a polymer, similar to plastic in its raw material origin, but it is engineered to biodegrade fully when composted. Unlike conventional plastic, it does not persist in the environment as microplastics.
Is PBAT safe to compost?
Yes. PBAT is certified compostable and must leave no harmful residues behind. The relevant certification standard now referenced in Australia for compostable packaging is EN 13432.
Does PBAT break down at home?
Yes. PBAT-based packaging is home compostable and designed to break down within 180 days in home compost conditions. Note that changes to Australian standards mean compostable mailers are no longer accepted in council green waste bins. Home composting is now the recommended end-of-life pathway.
What is the difference between PBAT and PLA?
PLA is a rigid, plant-derived bioplastic. PBAT is a flexible, petroleum-derived biodegradable co-polymer. In compostable packaging they are typically blended together , with PLA providing structure and PBAT providing flexibility and driving the composting process.
Is PBAT renewable?
Not fully. PBAT is partly derived from petroleum, making it non-renewable in its current form. Research into plant-based alternatives is ongoing.
HeapsGood Ecomailers are made from a PLA and PBAT blend, certified to Australian home and industrial compostable standards. Read the full breakdown of what our compostable mailers are made from, or explore the Ecomailers product page. For more on the science, see our blog post on PBAT. For more guides like this, visit the HeapsGood Knowledge Centre.