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PHA vs PLA: a buyer’s guide to compostable packaging
PLA was the default "compostable" plastic for more than a decade. It looks and works like conventional plastic, it runs on existing equipment, and it carries industrial composting certification. The catch is in that word industrial. Outside a hot composting facility, PLA breaks down very slowly, and regulators, composters and buyers have started to notice. PHA is the material many buyers are now weighing instead. This guide compares the two on the points that matter to a purchasing or sustainability decision.
What PLA is
PLA (polylactic acid) is made by fermenting plant sugars, usually from corn or sugarcane, into lactic acid, then joining that lactic acid into long chains through an industrial chemical process. It is clear, stiff and relatively cheap at scale, which is why it spread so fast into cups, lids, cutlery and clamshells.
Most PLA foodservice items are certified for industrial composting under ASTM D6400, which proves they compost in facilities that reach thermophilic (hot) temperatures. That certification says nothing about home compost, soil or water. Our post on what PLA is has more background.
What PHA is
PHA (polyhydroxyalkanoates) is a family of polyesters that bacteria make inside their own cells as an energy store. Instead of being assembled by chemical synthesis, the polymer is grown by microbes during fermentation, then extracted and formed into pellets. A 2025 review counts more than 300 bacteria with the ability to produce it.
Because PHA comes from biology, microbes in nature already carry enzymes that break it down. PlantSwitch makes its own PHA material, CompostZero™, made through fermentation from renewable feedstocks. Our complete guide to PHA covers how it is made and the different types.
How each one breaks down
PLA needs sustained heat
Microbes can't digest PLA's long chains directly. Water has to break them down first, and that step only moves quickly near PLA's glass transition temperature of roughly 55 to 60 °C. A 2022 paper in Polymers cites a 119-day compost study in which PLA reached 92.3% mineralization at 58 °C but only 14.9% at 25 °C, about the temperature of a backyard pile.
In the ocean, researchers at the Scripps Institution of Oceanography found that PLA did not degrade in seawater for over 428 days (PLOS ONE, 2023).
PHA is broken down by common microbes
Bacteria and fungi release enzymes called PHA depolymerases that cut PHA into small pieces they then use as food. A 2025 review in Frontiers in Microbiology lists PHA-degrading microbes in soils, freshwater and marine ecosystems. That is why PHA as a material biodegrades in soil, freshwater and marine environments, not only in compost, though rates vary and are slower in water than in soil.
The difference matters for real-world waste. Packaging escapes the bin it was designed for all the time. For the full science, read how compostable packaging actually breaks down.
PHA vs PLA side by side
| Question | PLA | PHA |
|---|---|---|
| How it is made | Lactic acid from fermented plant sugars, chemically joined into a polymer | Grown by bacteria during fermentation, then extracted |
| Typical certification | Industrial composting (ASTM D6400) | Can be certified home compostable (OK compost HOME) as well as industrially compostable |
| Home compost (about 25 °C) | Very slow: 14.9% mineralization in 119 days in one study | Breaks down at ambient temperatures |
| Soil and water | Slow without heat; no degradation in seawater over 428 days in the Scripps study | Biodegrades; PHA-degrading microbes are common in soil, freshwater and the sea |
| Fragments | Can linger where conditions stay cool | Remain food for microbes: No Forever Microplastics |
| Status as an organic input (USDA) | Not allowed; classed as synthetic | Not allowed; also classed as synthetic |
| Price | Generally lower, made at very large scale | Higher per kilogram today; production cost is the main barrier researchers cite |
What the rules mean for both materials
The USDA organic standards vote
In 2023 the Biodegradable Products Institute (BPI) petitioned the USDA to allow compostable plastics as feedstock in compost used on organic farms. The National Organic Standards Board's formal recommendation, dated January 14, 2026, voted 13 to 0 to classify these materials as synthetic and 0 to 13 against adding them to the National List. The board listed PLA and PHA among the main materials reviewed, and said it "remains open to reviewing synthetic compost feedstocks substance by substance."
California's compostable labeling law
California's law (AB 1201, now Public Resources Code section 42357) requires products labeled compostable to be made of materials allowed as inputs on organic farms under the USDA National Organic Program. CalRecycle extended the deadline to June 30, 2027. As things stand after the NOSB vote, neither PLA nor PHA qualifies, so the rule affects every compostable plastic sold in the state. BPI said in January 2026 that it was pursuing California legislation to change that link to the organic program. Check the current status before you finalize labels for California.
Claims and the FTC
The FTC's Green Guides treat an unqualified degradable claim as deceptive for items that won't fully decompose within a year of customary disposal. A PLA item sold as "biodegradable" with no qualifier is exposed under that rule. The safer approach for any material is to make the specific, certified claim and show the certificate.
Questions to ask before you switch
- Is the finished item certified home compostable, or only industrially compostable?
- Does the certificate name the product you are buying, and is it current?
- What does the supplier claim about soil, water or timing, and what certificate backs it?
- How will your labels hold up in California after June 30, 2027?
- Does the supplier make its own material, or buy resin from someone else?
- Can one supplier cover your cutlery, straws, stirrers and kits?
- Is the product FDA-compliant for food contact?
Distributors weighing a portfolio change can start with our distributor guide.
Getting CompostZero™ products
PlantSwitch is a material science company. We make the CompostZero™ material, develop each application and manufacture the finished product, so one supplier covers the whole chain. PlantSwitch products are certified home compostable, with certifications from TÜV Austria (OK compost HOME), BPI and DIN CERTCO, and they are FDA-compliant for food contact.
Shop cutlery kits and straws and stirrers, or ask about hot cups and lids, which are quote-only. PlantSwitch products are also available through distributor partners including Imperial Dade, Bunzl and Sysco; see our distributor page. To try them first, request samples or email sales@plantswitch.com.
Make the switch
