If PLA is the bioplastic you've already held, PHA is the one the industry is most excited about. These polyesters are grown inside microbes, and unlike most bioplastics they can break down in soil and even seawater, not just in an industrial composter.
| Property | PHB (homopolymer) | PHBV / PHBH (copolymers) |
|---|---|---|
| Melting point (Tm) | 170–180 °C | 120–160 °C |
| Glass transition (Tg) | 0–5 °C | −5 to 5 °C |
| Crystallinity | 55–80 % | Lower, tougher, less brittle |
| Tensile strength | 30–40 MPa | 20–35 MPa |
| Elongation at break | 3–8 % | up to 20–50 % |
| Density | 1.24–1.26 g/cm³ | ~1.25 g/cm³ |
Plain PHB is highly crystalline (55–80%), which makes it stiff and brittle with a narrow gap between its melting point and its decomposition temperature, a genuine processing headache. Adding a second monomer (giving PHBV or PHBH) lowers crystallinity and melting point, widening that processing window and boosting elongation from a brittle ~5% to a usable 20–50%. That's the whole reason the PHA family exists rather than just PHB.
PHA is unusual: it isn't synthesized in a reactor from monomers, it's farmed from bacteria. Feed certain microbes a rich carbon source, sugar, vegetable oil, even methane or captured CO₂, while starving them of a nutrient like nitrogen, and they start hoarding energy as tiny granules of PHA inside their cells, much as we store fat. Harvest the cells, extract the granules, and you have plastic. This is why PHA can be made from such varied feedstocks, including waste streams that would otherwise be a disposal problem.
The process is fermentation, then recovery. Microbes are cultured in large tanks under carefully controlled conditions that trigger PHA accumulation. The cells are then broken open and the polymer separated, washed, and dried. Recovery is one of the cost drivers, getting clean polymer out of biological cells at scale is harder than running a conventional chemical reactor, which is part of why PHA still costs more than PLA.
PHA is the family name. PHB (polyhydroxybutyrate) is the most common single member, stiff and rather brittle. PHBV and PHBH are copolymers that add a second unit to make the material tougher and easier to process. When someone says "PHA," ask which one, the properties vary a lot.
There's a second axis worth knowing, because it predicts a material's behaviour: chain length. Short-chain-length PHAs (3–5 carbons per monomer, like PHB) are highly crystalline, higher-melting, and brittle, more like a rigid plastic. Medium- and long-chain-length PHAs are lower-crystallinity, more flexible, and rubber-like. Producers effectively "programme" the material's character by controlling which monomers the microbes build, which is why the same microbial route can yield anything from a stiff tray to an elastic film.
One thing, mostly: it biodegrades almost anywhere. Where PLA needs an industrial composter, PHA can break down in home compost, in soil, and crucially in marine environments, which makes it the leading candidate for applications where leakage into nature is likely, like agricultural films or items that escape collection. It's also non-toxic and biocompatible, opening medical uses. Its properties can be tuned across a wide range by choosing the copolymer.
Cost and scale are the real story. PHA is meaningfully more expensive than PLA or fossil plastics, and large-scale production has a hard history, the bankruptcy of a major US PHA producer in 2025 was a reminder that the economics are unforgiving. Plain PHB is brittle and has a narrow processing window (it degrades if it gets too hot during moulding). "Marine biodegradable" is also still condition-dependent, it degrades far faster than conventional plastic, but "fast" can still mean many months. Promising material, genuinely hard business.
PHA has the broadest disposal profile of any mainstream bioplastic: industrial composting, home composting, soil, and marine biodegradation are all viable. That's its core selling point. The caveat is timeframe, biodegradation is a biological process and depends on temperature, moisture, and microbial activity, so it's never instant.
Related: PLA · Starch blends · Agriculture · Honest tradeoffs
PolyLoop is growing into a network across the whole chain: suppliers, manufacturers, recyclers, technology providers, converters, brands and buyers. Want to be featured as it grows? Tell us about your company.
Feature your company →