The Basics of ASTM Compostability Standards

When a compostable plate, cup, or bag claims industrial compostability in the U.S., almost every credible certification traces back to one of three ASTM standards: D6400, D6868, or D5338. These three documents — and a few companion specifications — are the technical foundation underneath the BPI certification mark, the CMA logo, and most state-level compostability labeling laws.

If you buy compostable products, sell them, or specify them for a business, you’ll eventually hit a moment where a supplier mentions “we’re ASTM D6400 compliant” and you need to know what that actually means. Or a customer asks why a different supplier’s “biodegradable” claim doesn’t satisfy you. Or a state regulator audits your packaging line. In all of those moments, the right answer requires understanding what the standards say and what they don’t.

This is a working explanation of the basics — written for the buyer, the operator, the compliance officer — not the polymer chemist.

What ASTM is and how a standard gets written

ASTM International is a 125-year-old standards body based in West Conshohocken, Pennsylvania. It develops and publishes voluntary consensus standards across roughly a dozen industries, from cement and steel to plastics and biopolymers. ASTM standards are not regulations themselves. They’re technical specifications that anyone — industry, regulators, certification bodies, courts — can adopt by reference.

A new ASTM standard goes through a multi-year drafting process inside a technical committee. For compostability, the committee is D20 (Plastics) and the subcommittee is D20.96 (Environmentally Degradable Plastics and Biobased Products). Members include resin manufacturers, packaging converters, composting facility operators, university researchers, and regulators. A draft gets balloted, revised, balloted again, and finally published after the committee reaches consensus. The whole process typically takes 5-7 years from initial proposal to first publication.

Standards are revised every 5-8 years. The current versions of the key compostability standards were last revised in 2019-2021.

ASTM D6400: the umbrella standard for compostable plastics

D6400 is the original and most-cited compostability standard. It applies to plastics that are designed to be composted in commercial composting facilities. The full title is “Standard Specification for Labeling of Plastics Designed to be Aerobically Composted in Municipal or Industrial Facilities.”

D6400 has three core requirements that a product has to pass:

1. Disintegration. Under composting conditions, no more than 10% of the original dry mass of the product can remain after 12 weeks, when tested in a 2mm sieve. In plain language: the product has to break into small enough pieces fast enough that the compost facility can process it on a normal schedule.

2. Biological breakdown. At least 90% of the organic carbon in the product must convert to carbon dioxide within 180 days under controlled lab conditions. This is the actual “biodegradation” measurement. It’s run using the methodology in ASTM D5338 (more on that below). The 90% threshold compares the test material to a control like cellulose — both should fully degrade in the same timeframe.

3. No ecotoxicity. The finished compost must not show toxic effects on plant growth (typically tested with cress, oats, or radishes) compared to compost without the test material. Heavy metals in the product are also limited — concentrations of regulated metals like arsenic, cadmium, lead, mercury, nickel, and selenium must be below specified maximum levels.

A product that meets all three becomes “D6400 compliant” — assuming the test was run by a qualified lab and reviewed by a certification body.

D6400 applies to: compostable cups, bowls, plates, food-service containers made from PLA, PHA, or other compostable plastics; compostable cutlery; compostable bags made from PBAT/PLA blends; compostable agricultural films.

ASTM D6868: the standard for paper coatings and films

D6868 covers materials where a non-plastic substrate (paper, board, sometimes natural fiber) is laminated or coated with a compostable plastic film. The full title is “Standard Specification for Labeling of End Items that Incorporate Plastics and Polymers as Coatings or Additives with Paper and Other Substrates Designed to be Aerobically Composted in Municipal or Industrial Facilities.”

D6868 was added because D6400 didn’t cleanly cover coated paper products. A paper hot cup with a PLA inner lining is half-paper, half-bioplastic. Same for kraft food containers with a PLA moisture barrier, or compostable trash bags with paper inner liners.

The pass criteria for D6868 are nearly identical to D6400 — same disintegration, biodegradation, and ecotoxicity thresholds. The difference is the test setup: D6868 tests the final composite product (paper plus coating) rather than the coating polymer alone.

D6868 applies to: compostable paper hot cups (with PLA or PHA lining); compostable take-out clamshells made from kraft board with a compostable barrier; compostable bag formats with multi-material composition; molded fiber products with secondary coatings.

A product can be both D6400 and D6868 compliant if it includes both pure-bioplastic and paper-bioplastic components in different parts.

ASTM D5338: the test method that backs the others

D5338 is not a product specification — it’s the lab methodology that’s used inside D6400 and D6868 to actually measure biodegradation. The full title is “Standard Test Method for Determining Aerobic Biodegradation of Plastic Materials Under Controlled Composting Conditions, Incorporating Thermophilic Temperatures.”

The method works like this:

1. A test specimen of the candidate material is placed in a sealed bioreactor along with a standard quantity of mature compost inoculum.
2. The bioreactor is held at 58°C (the thermophilic phase of industrial composting) with controlled humidity, oxygen supply, and CO₂ measurement.
3. The carbon dioxide evolved over time is measured continuously and compared to a parallel control with cellulose as the test material.
4. The test runs for up to 180 days. Pass: ≥90% of the carbon in the specimen has been converted to CO₂ by the end.

D5338 results are the input to D6400 and D6868 certification. A lab can’t certify a product without running the D5338 test (or an equivalent ISO 14855 test).

The 58°C requirement is important to understand: D5338 simulates the hot phase of a commercial composting operation. It does not simulate backyard composting, home compost piles, or marine environments. A D5338-passed material is not guaranteed to biodegrade outside of industrial conditions.

D6691, D5511, D7081: the cousins

A few related ASTM standards extend or branch off from the main three:

D6691 — biodegradation of plastic materials in the marine environment. A separate test that runs under simulated seawater conditions. Almost no compostable food-service items currently pass D6691, despite occasional marketing claims. PHA-based polymers are the leading candidate to eventually pass this standard, but it’s still mostly aspirational.

D5511 — biodegradation under high-solids anaerobic-digestion conditions. Tests biodegradation in environments like landfills with limited oxygen. Some “landfill-biodegradable” claims reference this standard, but the test conditions don’t reflect actual landfill conditions well, and the standard has been controversial. The FTC Green Guides specifically caution against landfill-biodegradability claims.

D7081 — discontinued. Was used briefly for marine biodegradability before D6691 superseded it.

D8410 — relatively new (2021). Specification for compostable plastics used in agricultural mulch films. Covers a different application but uses similar testing methodology.

How ASTM standards become BPI certification

The BPI (Biodegradable Products Institute) certification mark is the most common compostability label on U.S. products. The path from “ASTM-compliant” to “BPI-certified” works like this:

1. The manufacturer submits the product to one of BPI’s approved testing labs (Eden Research, NSF, OWS, Intertek, and a few others).
2. The lab runs the D5338 biodegradation test, the D6400 or D6868 disintegration test, and the ecotoxicity testing per the relevant standard.
3. The lab issues a report to BPI documenting the results.
4. BPI’s technical committee reviews the report and verifies compliance.
5. BPI certifies the product and the manufacturer can use the BPI logo on packaging.

BPI certifications are product-specific. A manufacturer can’t say “all our products are BPI-certified” just because one SKU passed. Each SKU goes through testing separately, with its own certificate number.

BPI certifications are also renewable. Most run for 2-3 years before requiring re-testing or recertification. Buyers should ask suppliers for current certificates with the specific SKU and an expiration date.

Where the standards fall short

ASTM standards are technically rigorous, but they have known limitations that matter in real-world use:

Lab conditions vs. real composting facilities. D5338 runs at 58°C with controlled inoculum and humidity. Real composting facilities run at variable temperatures, with variable moisture, processing different mixed loads at different speeds. A material that passes D5338 may take longer to compost in some facilities, or fail to compost completely in others where the thermophilic phase is shorter. The CMA (Compost Manufacturing Alliance) certification was created specifically to test in field conditions because of this gap.

180-day test window. Some commercial composting operations run on 60-90 day cycles, not 180. A material that passes the standard but takes the full 180 days might end up in finished compost as residual fragments — visible to a hauler doing quality control, even if it’s still chemically biodegrading.

No standard for home composting in the U.S. D6400 is industrial only. European standards EN 13432 and EN 14995 cover industrial, and there’s a separate spec (TUV OK Compost HOME) for backyard conditions. The U.S. hasn’t adopted an equivalent home-compostable standard, which is why home-compostable claims on U.S. packaging usually reference European certifications instead.

Marine and freshwater gaps. D6691 exists but the threshold and testing protocols have known issues. Materials that pass D6400 routinely don’t pass D6691 — meaning a “compostable” product is not “ocean-degradable” or “freshwater-degradable” in any practical sense. This matters for litter assessment but is often glossed over in marketing.

Microplastics. The standards measure breakdown to a 2mm sieve. Particles smaller than 2mm pass the test even if they’re not fully biodegraded. Research is ongoing about whether intermediate fragments persist in finished compost or in agricultural soil where compost is land-applied. The standards don’t currently address this.

Per- and polyfluoroalkyl substances (PFAS). D6400 and D6868 don’t directly test for PFAS in the product. Several states (California, Washington, Maine, New York) now require PFAS-free certification separately from compostability certification. BPI added PFAS restrictions to its own certification criteria in 2020, and the next generation of ASTM standards is likely to incorporate this.

How to actually use the standards as a buyer

If you’re buying compostable products for a restaurant, retail store, or institution, the standards are most useful as the bedrock that supports the claims on the package. Practical guidance:

Demand the specific ASTM compliance number with the SKU. “Our products are D6400 compliant” is a weak claim. “This 32-oz hot cup, SKU EC-HC32, is D6400 and D6868 compliant per BPI certificate #BPI-12345” is a strong claim. Get it in writing.

Verify the certificate is current. BPI publishes a searchable certification list at bpiworld.org. Look up the certificate number. Check the expiration date. If a supplier shows you a 2020 certificate in 2025, that’s a red flag.

Match the standard to the product. D6400 for pure-plastic items, D6868 for paper-and-coating items. A product made entirely of bagasse pulp (no coating) may not need either standard — it’s a paper product and certifies under different criteria.

Ask about state-specific requirements. Several states now have packaging laws that go beyond ASTM compliance. California’s SB 343 restricts the chasing-arrows recycling symbol; California’s AB 1201 restricts compostability claims unless products meet specific criteria including state-approved certification. Washington and Maine have similar laws. The ASTM standards are necessary but not sufficient in these states.

Don’t accept “biodegradable” as equivalent. The FTC Green Guides explicitly state that “biodegradable” without context is deceptive. ASTM compliance gives you compostability under specific conditions — not unlimited biodegradability. A product label that says “biodegradable” without naming the standard or condition is making a weaker claim than ASTM compliance, despite often sounding stronger.

How to use them as a supplier or specifier

If you’re on the other side — selling compostable products or specifying them for a business operation — the standards are your defensible record:

• Run testing through an accredited lab. Don’t accept supplier self-claims of ASTM compliance without third-party lab reports.
• Keep certificates current and on file. The compliance officer who shows up after a customer complaint will want to see the paper.
• For institutional buyers (school districts, hospitals, government agencies), include ASTM compliance language in your RFP boilerplate. Pulls out the suppliers who can’t document.
• For products that touch food, look for FDA food-contact compliance in addition to ASTM compostability. The two are separate.

Where this matters in practice

The standards do real work in real situations. A composting facility operator can refuse a load that contains products without recognizable certification — they’re not obligated to take the word of a “compostable” claim without proof. A buyer for a hospital network can specify D6400 compliance in a 10-million-unit RFP and use the standard to disqualify suppliers. A municipal agency rolling out commercial composting can write the standards into the ordinance language.

This is also true for everyday product selection. When you’re choosing among compostable food containers, bowls, cups and straws, utensils, or bags for a business operation, the ASTM-compliance documentation is what separates real compostable products from greenwashed ones. Ask for it. Read the certificate. Verify against BPI’s database.

The takeaway

ASTM D6400, D6868, and D5338 are not the most exciting documents in the world to read, but they’re the technical reason that compostability claims on U.S. products have any rigor at all. They define what “compostable” means in measurable terms: 90% biodegradation in 180 days at 58°C, with no toxic residue and visible disintegration in 12 weeks. Anything that doesn’t pass that bar isn’t compostable in the technical sense, regardless of marketing copy.

If you understand the basics of these three standards, you understand most of what underlies the compostable-products industry in North America. You can evaluate supplier claims. You can challenge greenwashing. You can specify packaging that actually composts where you say it will.

The standards are imperfect — they don’t cover home composting, marine biodegradation, or microplastics. But they’re the floor, not the ceiling. Newer standards and certifications (CMA field testing, TUV OK Compost HOME, state-level PFAS rules) build on top of this foundation rather than replacing it. Get the basics right and the rest of the certification landscape becomes much easier to navigate.

One last practical point: when you encounter a product that claims compostability but doesn’t reference a specific ASTM standard or a certification body that uses one, treat it the same way you’d treat any unverified claim. Ask for the certificate. Ask for the SKU-level documentation. Ask which lab ran the testing. The suppliers who can answer cleanly are the ones worth buying from. The ones who deflect, generalize, or send vague brochures are the ones who tend to disappear from the market the next time a state regulator tightens enforcement. The standards aren’t just technical specifications — they’re a practical filter that separates serious operators from opportunistic ones.

For B2B sourcing, see our compostable supplies catalog or compostable bags catalog.

Verifying claims at the SKU level: ask suppliers for a current Biodegradable Products Institute (BPI) certificate or an OK Compost mark from TÜV Austria, and check that retail-facing copy meets the FTC Green Guides qualifier requirement on environmental claims.