How to Read a Compostability Test Report

A compostability test report is the underlying document that backs every BPI certification, every TÜV OK COMPOST mark, every claim that a product meets ASTM D6400 or D6868. It’s the technical evidence that a third-party lab actually composted samples of your product (or a competitor’s product) and observed the required behavior, disintegration within 12 weeks, biodegradation above 90% of theoretical CO2 production, no negative effect on plant growth from the resulting compost, and heavy metals below regulatory limits.

For most people working with compostable foodware, the test report sits behind a certification mark and never gets opened. The BPI logo on the package is shorthand for “this passed the tests”; the underlying 40-80 page lab report stays on the manufacturer’s server. But for procurement professionals doing supplier due diligence, sustainability consultants verifying client claims, regulatory affairs teams responding to EPA or FTC inquiries, and competitive intelligence professionals comparing competitive products, reading the actual report is essential.

This article walks through how to read a compostability test report, what’s in each section, what to verify, what’s normal and what’s a red flag. The structure applies primarily to ASTM D6400 (compostable plastics) and ASTM D6868 (compostable coatings on natural substrates) reports from major North American labs (Eden Research Labs, OWS, NSF Sustainability). European EN 13432 reports follow a similar but distinct structure. ISO 17088 reports are most similar to D6400.

What the report should physically look like

A complete ASTM D6400 test report from a reputable lab is typically 40-80 pages, including:

• Cover page with sample identification and test summary
• Table of contents
• Sample description and pre-test characterization (5-10 pages)
• Test methodology by section per ASTM standard (15-30 pages)
• Test results with data tables and graphs (15-25 pages)
• Conclusions and pass/fail by criterion (3-5 pages)
• Appendices including raw data, photographs, instrument calibration records (5-15 pages)

Reports shorter than 30 pages are suspect. Reports longer than 100 pages are typical when the lab includes extensive raw data appendices.

The report should be on the lab’s letterhead, signed by the lab director or principal scientist, and dated. The signature and date matter, unsigned, undated reports are not acceptable for certification submissions.

Section 1: Sample description

The first substantive section identifies what was tested. Read this carefully, it’s the foundation of everything else.

The sample description should specify:

• Sample name and identification. Should match the product name exactly. If the report says “Sample CB-2024-001” and the product is “World Centric Bagasse Bowl 16oz,” verify those are the same product.
• Material composition. Should list all material inputs by weight percent. Percentages should sum to 100%. Any material at 1%+ should be individually identified.
• Source of samples. Should specify the manufacturing batch or production run from which samples were taken. Reputable reports describe sample handling from manufacturer to lab.
• Sample form. Whole product, sample cut from product, or compressed pellets. ASTM D6400 testing requires testing of the final-form product, not raw resin or sample cut-offs. If the report tests pellets rather than finished product, it’s testing the resin, not the product, that’s a different (and less rigorous) test.

Red flags in this section:

• Sample identification doesn’t match the product you’re verifying
• Material composition is vague (“compostable plastic resin”) rather than specific (PLA 60%, bagasse 30%, starch binder 10%)
• Percentages don’t sum to 100%
• Sample form is pellets/resin rather than finished product (only valid for resin certifications, not product certifications)

Section 2: Pre-test characterization

Before the actual composting test, the lab performs baseline characterization of the sample. This should include:

• Physical dimensions (length, width, thickness, weight). Establishes baseline against which post-test disintegration is measured.
• Density (g/cm³). Affects how the sample behaves in composting conditions.
• Thermal analysis (typically DSC, differential scanning calorimetry) showing the sample’s melting point and crystallinity. Important for understanding how the sample will behave at composting temperatures.
• Heavy metals analysis before testing. Heavy metals (lead, cadmium, mercury, arsenic, chromium, copper, nickel, selenium, zinc, molybdenum) must be below ASTM limits. Pre-test analysis confirms the sample meets these limits as-manufactured.

Red flags in this section:

• Heavy metals data is missing or incomplete (all 10 metals listed in ASTM D6400 should be reported)
• Any heavy metal exceeds the ASTM limit (limits vary by metal; the report should explicitly state limits and measured values)
• Pre-test characterization is brief or skipped entirely

Section 3: Test methodology

This section describes how the test was actually conducted. It should reference ASTM D6400 (or the relevant standard) section by section and confirm the lab followed each required step.

Key elements to verify:

• Compost source. ASTM D6400 requires composting in mature compost from an active industrial composting facility. The lab should specify which facility provided the inoculum compost.
• Temperature profile. Industrial composting test conditions require maintaining specific temperatures (typically 58°C ± 2°C for the thermophilic phase). The report should show actual temperature data, not just claim compliance.
• Moisture content. Compost moisture should be maintained at 55-60% throughout testing. Report should show moisture measurements.
• Aeration. Compost should be aerated to maintain aerobic conditions. Report should describe aeration system used.
• Test duration. Disintegration test runs 12 weeks; biodegradation test runs up to 180 days. Report should specify actual test duration for each test.

Red flags in this section:

• Compost source not specified or sourced from a non-industrial facility
• Temperature data missing or shows temperatures outside the required range
• Aeration system not described or test conducted under anaerobic conditions
• Test duration shorter than ASTM minimums

Section 4: Disintegration test results

The disintegration test measures how much of the sample physically breaks down within 12 weeks of composting. ASTM D6400 requires ≥90% of the sample mass to disintegrate to particles smaller than 2mm within 12 weeks.

The report should show:

• Initial sample mass at the start of the test
• Sample mass remaining at each measurement point (typically week 2, 4, 6, 8, 10, 12). Mass should decrease over time as the sample disintegrates.
• Particle size analysis at week 12, showing what fraction of remaining sample is larger or smaller than 2mm
• Photographs of samples at week 0, week 6, and week 12 minimum. Photos provide visual evidence of disintegration progression.
• Pass/fail determination based on whether ≥90% of original mass has disintegrated to <2mm particles

Red flags in this section:

• Mass measurements at only one or two timepoints (should be 5-6 timepoints minimum)
• No photographs included
• Particle size analysis vague or missing
• Pass/fail determination doesn’t match the data (claims pass but data shows <90% disintegration)

Section 5: Biodegradation test results

The biodegradation test measures how much of the sample’s carbon is converted to CO2 by microbial activity (versus remaining as recalcitrant carbon). ASTM D6400 requires ≥90% biodegradation within 180 days, measured as a percentage of theoretical CO2 production from the sample’s carbon content.

The report should show:

• Carbon content of sample (typically measured by elemental analysis before testing). Used to calculate theoretical CO2.
• Theoretical CO2 production based on sample carbon content
• Actual CO2 production over time in the test reactor, measured continuously or at frequent intervals
• Reference cellulose CO2 production in a parallel reactor (cellulose is the positive control; if cellulose doesn’t biodegrade in your reactor, your sample test isn’t valid either)
• Biodegradation curve showing percent biodegradation over time
• Pass/fail determination based on whether ≥90% biodegradation was achieved within 180 days

Red flags in this section:

• Reference cellulose biodegradation is missing or below 70% (suggests the test reactor isn’t functioning properly)
• Biodegradation curve shows unusual plateaus or drops (suggests measurement issues or sample inhibiting microbial activity)
• Pass/fail determination doesn’t match the data
• Theoretical CO2 calculation isn’t shown or isn’t transparent

Section 6: Plant toxicity test results

After composting, the resulting compost (containing the disintegrated sample residue) must not negatively affect plant growth. ASTM D6400 requires the compost to support plant growth at least 90% as well as control compost (compost without the sample residue).

The report should show:

• Plant species used (typically two species, often cress and barley or similar)
• Growth metrics measured, seedling emergence rate, plant biomass at harvest, growth rate
• Comparison to control compost for each metric
• Pass/fail determination based on whether plant growth in sample compost is ≥90% of control compost

Red flags in this section:

• Only one plant species tested
• Growth metrics vague or measured at only one time point
• Pass/fail determination doesn’t match the data (sample compost supports significantly less plant growth but report claims pass)

Section 7: Heavy metals in finished compost

After composting, the finished compost containing the sample residue is analyzed for heavy metals. The compost should meet the same ASTM heavy metals limits as the pre-test sample.

The report should show:

• Heavy metals concentrations in finished compost for all 10 ASTM-listed metals
• Comparison to ASTM limits for each metal
• Pass/fail determination based on whether all metals are below limits

Red flags in this section:

• Missing metals (should be all 10)
• Any metal exceeds the limit (rare but does happen; should be a clear fail)

Section 8: Conclusions

The conclusions section summarizes pass/fail for each test and states whether the sample meets ASTM D6400 overall. A clean pass should show:

• Disintegration: ≥90% to <2mm within 12 weeks (PASS)
• Biodegradation: ≥90% within 180 days (PASS)
• Plant toxicity: ≥90% of control growth (PASS)
• Heavy metals (pre-test and finished compost): below ASTM limits (PASS)
• Overall: PASS, meets ASTM D6400

Red flags in the conclusions:

• Overall PASS without clear individual test PASS for all criteria
• Conclusion language hedges (“substantially meets,” “approximately compliant,” “in most respects meets”), ASTM compliance is binary, not approximate
• Conclusion doesn’t match the data in earlier sections

Common report problems and what they mean

A few common problems in test reports and how to interpret them:

“Sample tested as pellets, not finished product.” This is a resin certification, not a product certification. The resin may compost; the final product may behave differently due to coatings, additives, or processing. Don’t accept this as evidence of product compostability.

“Test conducted under home-compost conditions, not industrial.” Home compost testing follows different standards (ASTM D7081 in the US, TÜV OK HOME in Europe). A home-compost report doesn’t certify industrial compostability and shouldn’t be used to claim BPI certification.

“Test duration extended to 24 weeks instead of 12.” ASTM D6400 disintegration requires 90% disintegration within 12 weeks. Extending to 24 weeks and then claiming pass is a workaround, not compliance. Some certifications accept this; many don’t. Read the certification’s specific requirements.

“Coating layer tested separately from substrate.” ASTM D6868 (for coated paper products) tests the whole product, not just the coating. A report testing the coating in isolation isn’t D6868-compliant.

“Replicate analysis missing.” ASTM testing requires multiple replicate samples (typically 3-5) for statistical validity. A report based on single-sample data isn’t statistically valid.

Verifying the lab itself

Beyond the report content, verify the lab:

• Accreditation. Reputable testing labs are ISO/IEC 17025 accredited for the specific tests they’re performing. The accreditation should be cited in the report.
• Lab reputation. Eden Research Labs, OWS, NSF Sustainability are the three commonly used labs in North America. Test reports from other labs may be legitimate but warrant additional verification.
• Direct verification. For high-stakes verification (regulatory inquiry, major supplier qualification), contact the lab directly to confirm the report is genuine. Counterfeit test reports do exist in the compostable industry.

Using the report for procurement decisions

For procurement teams using test reports to qualify suppliers:

1. Request the full report, not just the certification summary. A supplier unwilling to share the full report is a red flag.
2. Verify the report covers the specific product you’re buying, not a related product.
3. Check the report date. ASTM standards evolve; reports older than 5 years should be verified for current standards compliance.
4. Match the report’s tested product to the product you’ll receive. Confirm the manufacturer hasn’t changed material composition, supplier, or process since testing.
5. Keep the report on file for your own regulatory compliance and customer inquiries.

What the report enables

A well-read compostability test report enables:

• Confident product claims in marketing and customer communications
• Regulatory compliance with state and federal sustainability requirements
• Supplier qualification with technical basis rather than marketing claims
• Competitive intelligence, reading competitor product reports reveals their actual material composition and performance
• Customer transparency, sharing test reports with sustainability-conscious customers builds credibility

For procurement of compostable food container, compostable cups and straws, and other compostable foodware, requesting and reading the underlying test reports, not just trusting the certification logo, is the gold standard for supplier due diligence.

A practical checklist for first-time report readers

When you open your first compostability test report:

1. Verify the sample identification matches the product you care about
2. Check material composition disclosure for completeness
3. Verify heavy metals data is present and below limits (pre-test)
4. Confirm test methodology cites the correct ASTM standard
5. Check disintegration test data shows ≥90% within 12 weeks
6. Check biodegradation test data shows ≥90% within 180 days
7. Check plant toxicity test data shows ≥90% of control
8. Verify finished compost heavy metals below limits
9. Confirm conclusions match the data
10. Verify lab accreditation and signature

That’s the basic competency for reading a compostability test report. Each subsequent report becomes faster as you build pattern recognition for what good reports look like versus what gaps and red flags look like. Within 5-10 reports, you’ll be able to assess a 60-page document in 15-20 minutes.

The investment is worth it. Compostable industry decisions are increasingly made on technical evidence rather than marketing claims, and the people who can read the underlying evidence make better decisions.

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

For procurement teams verifying compostable claims, the controlling references are BPI certification (North America), EN 13432 (EU), and the FTC Green Guides on environmental marketing claims, these are the only sources U.S. enforcement actions cite.