Are you confused—like many across the industry and supply chain—about how U.S. chemical companies use the mass balance approach versus physical bio-based methodology in their net‑zero and sustainability claims? You’re not alone. This is one of the most common sources of misunderstanding (and sometimes skepticism) in the sector. The debate centers on two approaches: the dominant mass balance method (leading to “bio‑attributed” claims) and the less common physical bio‑based methodology (which delivers measurable biogenic content).
Most major U.S. producers rely on mass balance, typically certified under ISCC PLUS, to scale renewable transitions without rebuilding existing infrastructure.
Mass Balance (Bio‑Attributed)
In the mass balance approach, bio-based or recycled feedstocks—such as corn, soybean or sugarcane derivatives, or used cooking oil—are blended into fossil‑based production systems like steam crackers. Sustainability benefits are then allocated through audited bookkeeping, allowing equivalent renewable volumes to be credited to specific outputs.
Products are labeled “bio‑attributed via certified mass balance,” often with disclaimers noting that the physical molecules in the final product may still be predominantly fossil‑derived (which can be confirmed through ¹⁴C testing). Despite this, the method is scalable, cost‑effective, and enables real upstream fossil displacement, with verified GHG reductions of 50–90% per attributed ton. It also supports SBTi‑validated Scope 3 targets and aligns with the 2025 Chemicals Sector Pathway’s Decarbonization Contribution Percentage (DCP) metric.
Physical Bio‑Based
Physical bio‑based methodology, by contrast, uses segregated or dedicated systems so that biogenic carbon remains detectable in the final product via radiocarbon testing (e.g., ASTM D6866). This enables straightforward claims such as “X% bio‑based” (including USDA BioPreferred labeling). While this approach offers clearer, more intuitive proof of renewability, it is harder to scale within today’s integrated fossil‑based infrastructure because it requires dedicated equipment and often significant capital investment.
ISCC PLUS and Regulatory Context
ISCC PLUS is a voluntary certification scheme developed by the International Sustainability and Carbon Certification (ISCC) system. Unlike ISCC EU, which supports legally mandated sustainability requirements for biofuels under the EU Renewable Energy Directive (RED II), ISCC PLUS applies to non‑regulated markets.
The mass balance approach supports SBTi‑validated targets by enabling companies to attribute emissions reductions to alternative feedstocks through audited chain‑of‑custody systems. The SBTi Chemicals Sector Pathways (updated December 2025) emphasize measurable reductions in emissions intensity and increased use of alternative carbon sources—without mandating any specific chain‑of‑custody method—preserving flexibility for implementation.
USDA BioPreferred and ASTM D6866
In the USDA BioPreferred Program, biobased content thresholds define the minimum percentage of renewable biological material required for a product to qualify. These thresholds are measured using ASTM D6866, which determines the ratio of new organic carbon (from renewable sources) to total organic carbon, excluding water and inorganic carbon.
It is important to distinguish between “bio‑attributed” (mass balance) and “bio‑based” (physical content). ASTM D6866 is the verification method that differentiates physical biogenic content from attributed claims.
Industry Debate
There is no single “right” approach. The mass balance method—pragmatic and independently audited—faces criticism from groups such as the Natural Resources Defense Council (NRDC) for potentially enabling greenwashing, given the fossil‑dominant physical composition of many end products. Proponents counter that mass balance is essential for accelerating meaningful progress toward net zero without waiting decades for new infrastructure.
When evaluating suppliers, it is best to prioritize:
- ISCC PLUS certification
- USDA BioPreferred labeling (where applicable)
- Clear, transparent disclaimers
- Third‑party audit documentation
In the end, both mass balance and physical bio‑based approaches play essential but distinct roles in the chemical sector’s decarbonization journey. Understanding how each method works—and what its claims truly represent—allows companies and buyers to make informed, credible decisions as the industry transitions toward lower‑carbon feedstocks.
