PHA bioplastics: what they are and how they are used

By the Compost Ready editors · Updated 12 October 2026

PHA, short for polyhydroxyalkanoates, is a family of polyesters that bacteria build inside their cells. Extract it and you get a plastic that can be moulded, blown into film or coated onto paper, and that microbes can later break down again.

What is PHA?

Many bacteria do something similar to what we do with fat. When they have plenty of carbon to eat but run short of another nutrient, such as nitrogen or phosphorus, they stop growing and stockpile the carbon instead. The stockpile takes the form of polymer granules inside the cell. Those granules are PHA.

The first one to be identified was poly(3-hydroxybutyrate), PHB, described by the French microbiologist Maurice Lemoigne at the Pasteur Institute in the mid-1920s, in the bacterium Bacillus megaterium. Since then well over a hundred different building blocks have been found in PHAs, which is why the name covers a whole family rather than one material.

For packaging, two members matter most:

• PHB is stiff and has a fairly high melting point, but it is brittle, and it can degrade during processing because the window between melting and breaking down is narrow.
• PHBV adds hydroxyvalerate units to the chain. More hydroxyvalerate generally makes the material tougher and easier to process. Most recent food packaging research uses PHBV.

How PHA is made

Production looks more like brewing than like a petrochemical plant. The bacteria stores the polymer only under the right feeding regime, so the process usually runs in stages:

1. Grow the culture. Bacteria are fed a carbon source, often sugars, plant oils or fatty acids.
2. Trigger accumulation. Limit a nutrient so the cells switch from growing to storing. In good conditions, PHA can make up most of the cell's dry weight.
3. Extract and purify. The cells are broken open and the polymer is separated, washed and dried into powder or pellets.
4. Compound. Like any plastic, raw PHA is blended with additives or other polymers before it is moulded or made into film.

The carbon source is the expensive part, which is why researchers have spent years testing cheaper feedstocks. Cheese whey, fruit pulp left over from juice making and the organic fraction of municipal waste have all been turned into PHBV in published studies. Using a waste stream cuts cost and gives an awkward by-product a use. We follow the whey route in detail in how to make food packaging from cheese whey.

Properties that matter for food packaging

PHA is often compared with polypropylene, because the two have broadly similar stiffness and melting behaviour. In practice, packaging engineers care about a few specific things.

Barrier. PHBV blocks water vapour reasonably well for a bioplastic, but on its own its oxygen barrier isn't good enough for oxygen-sensitive foods such as fresh meat. That's why research projects combine it with high-barrier layers. One YPACK study paired PHA films with cellulose nanocrystal interlayers to raise the oxygen barrier.

Toughness. PHB is brittle, and pure films can crack. Copolymers, blends and natural fibres are used to fix this.

Heat sealing. A flow-pack bag has to seal on a fast packing line. Researchers have developed electrospun PHBV layers that work as heat-sealing ("hot-tack") layers in multilayer films.

Active functions. PHA layers can carry natural antimicrobials such as oregano essential oil or eugenol, or oxygen-scavenging particles. More on that in active packaging.

How PHA breaks down

Many microorganisms in nature produce enzymes that can break PHA down, which makes sense: they evolved to use it as food. That's the main reason PHA is studied for breakdown in soil and water as well as in compost, while PLA is mainly designed for industrial composting.

Some caution is still needed. Breakdown speed depends heavily on thickness, temperature and the microbes present, and there is no general European standard for biodegradation in the sea. A PHA claim, like any other, should name the standard and environment it was tested in. The same packaging rules apply too: in EU law, a PHA cup is still a plastic product under the single-use plastics directive.

Research on PHA food packaging

PHA packaging has moved from lab curiosity to pilot lines over the last decade, and EU research funding has been a big part of that. The YPACK project, coordinated by the Spanish research council CSIC, ran from November 2017 to April 2021 with a total budget of about €7.3 million, of which the EU contributed about €6 million. Its goal was to take two PHA-based formats to pre-industrial scale: a multilayer thermoformed tray with an active inner layer, and a multilayer flow-pack bag with an improved barrier. Both used PHBV and fillers from food-industry by-products, namely cheese whey and almond shells, and were tested with fresh meat, fruit and vegetables.

The project's published papers cover, among other things, PHBV biopapers made from cheese whey, films from fruit pulp waste, antimicrobial PHBV layers with essential oils, and high-oxygen-barrier multilayers. We list them, with short summaries, on our publications page, and give an independent overview of the project on About YPACK.

Cost and availability

The honest summary is that PHA works but costs more. Reviews of PHA packaging consistently name high production cost and some weaker mechanical properties as the main reasons it hasn't displaced conventional plastics. Waste feedstocks and better processing are the two levers researchers are pulling. For now, you are most likely to meet PHA in niche items, coatings and blends rather than as the standard tray in a supermarket.