What is PBAT? The flexible compostable polymer explained

If you've used a compostable bag that stretches, seals and doesn't split the moment you overfill it, there's a good chance PBAT is part of the reason. It's the quiet workhorse of flexible compostable packaging. Here's what it is, what it isn't, and how to dispose of it.

What is PBAT?

PBAT stands for poly(butylene adipate-co-terephthalate). That's a mouthful, so most people stick to the acronym. It's a type of polyester known as a copolyester, and it's designed to be broken down by microbes.

A quick note on where it comes from, because it's often misreported: PBAT is made from fossil-based ingredients. It isn't plant-derived. What makes it different from conventional plastic isn't its origin, it's its ending. PBAT is built to biodegrade into carbon dioxide, water and biomass in compost, rather than hanging around for generations.

Why PBAT is in so many compostable products

PBAT's big talent is flexibility. It's soft, it stretches, and it resists tearing, which is what you want in a film or bag. Other compostable materials, such as PLA, are stiffer and can be brittle on their own. So PBAT is often blended with PLA, corn starch or minerals to get the right balance of strength, stretch and feel.

Two ZERO examples:

• ZERO Resealable Food Storage Bags are made from PBAT, corn starch and calcium carbonate. There's no PLA in them.
• ZERO Cling Wrap is mainly PLA made from sugarcane, with about 20% PBAT added for stretch.

For a side-by-side look at the two materials, see PLA vs PBAT.

How does PBAT break down?

It happens in two stages. First, water breaks the bonds in PBAT's long chains (a process called hydrolysis), cutting them into shorter pieces. Then microbes, especially bacteria and fungi, use enzymes to digest those pieces into carbon dioxide, water and biomass. Researchers have identified the specific microorganisms and enzymes involved in PBAT biodegradation, so the pathway is well understood.

How quickly it happens depends on conditions (warmth, moisture, microbes) and on the product itself, including its thickness and what it's blended with. That's exactly why certification matters: it tests the finished product, not just the raw material.

Home compostable or industrial?

Not every PBAT product is the same. Some are certified only for industrial composting. Others are tested and certified to break down in a home compost bin.

• AS 5810 is the Australian standard for home compostable plastics.
• AS 4736 is the Australian standard for industrially compostable plastics.
• TÜV Austria OK compost HOME is a widely recognised international home composting certification.

ZERO Resealable Food Storage Bags are certified home compostable (TÜV Austria OK compost HOME), so you can put them in your home compost. If you don't compost at home, check whether your council's FOGO bin accepts certified compostable packaging.

Want to know more about the two standards? Read home compostable vs industrial.

Pros and cons of PBAT

What it does well

• Gives compostable films and bags the flexibility and tear resistance people expect.
• Biodegrades into carbon dioxide, water and biomass in compost.
• Can be certified home compostable when the finished product passes testing.
• Works on existing film-making equipment.

The honest trade-offs

• It's fossil-based, so it doesn't offer the renewable-feedstock benefit of plant-based materials.
• It costs more to make than conventional plastic film.
• Like any compostable material, it needs to actually reach compost. In the ocean or as litter, it won't do its job well.

ZERO's long-term goal is to move completely away from petroleum-based polymers through our own materials R&D. Until then, certified home compostable blends are the best option we have for flexible bags.

What about soft plastics recycling?

PBAT doesn't belong in soft plastics recycling. It's chemically different from the polyethylene those programs were built for. The big supermarket soft plastics drop-off program, REDcycle, collapsed in 2022, so what's available near you may have changed. If you want the latest, see our guide to soft plastics recycling in Australia.

For certified compostable PBAT products, the answer is simpler: compost them.

How to dispose of PBAT products

1. Check the label for a certification mark and whether it says home or industrial.
2. Home compostable? Put it in your home compost. Tearing it into smaller pieces helps it break down faster.
3. Industrial only? Check your council's FOGO rules for certified compostable packaging.
4. Keep it out of kerbside recycling and soft plastics collection.

The easy swap

If you go through zip-lock bags for school lunches, leftovers or the freezer, ZERO Resealable Food Storage Bags (snack, sandwich and storage sizes, from $4.99) are a simple change. They're made from PBAT, corn starch and calcium carbonate, tested for food contact, freezer-friendly and certified home compostable. Same job, better ending.

FAQ

Is PBAT plant-based?

No. PBAT is made from fossil-based ingredients. It's designed to biodegrade in compost, which is what sets it apart from conventional plastic.

Is PBAT home compostable?

It depends on the finished product. ZERO's bags containing PBAT are certified home compostable (TÜV Austria OK compost HOME).

Can PBAT go in soft plastics recycling?

No. Compost certified PBAT products instead.

Do ZERO bags contain PLA?

No. ZERO Resealable Food Storage Bags are made from PBAT, corn starch and calcium carbonate.