What Is Mass Balance Accounting?
Mass balance is not a new concept developed for advanced recycling. It is an established accounting approach that has been used for years in energy, agriculture, forestry, textiles, and other sectors to track material attributes through complex manufacturing or supply chains. It is designed to help account for how much recycled or certified material enters a system and how that material is attributed to outputs produced from the process.
Similar accounting approaches are already used in a variety of industries and supply chains, including:
renewable electricity,
sustainable aviation fuel,
cocoa,
palm oil,
timber/forestry products, and
cotton
Mass balance accounting is used when material inputs from multiple sources move through shared infrastructure or complex supply chains in which physical separation of the novel and conventional feedstock sources is not practical.
Why is Mass Balance Accounting Part of the Plastic Recycling Conversation?
In many manufacturing systems, recycled and virgin raw materials are processed together within the same equipment and infrastructure because separating these materials into entirely different production lines is not practical or feasible. In petrochemical and polymer manufacturing, materials are processed through large-scale, integrated infrastructure designed to optimize efficiency, product quality, and economics.
Mass balance accounting is also receiving increased attention from policymakers, regulators, certification organizations, and industry stakeholders as governments consider recycled-content requirements, environmental claims, and broader circular economy policies. As a result, discussions about how mass balance should be defined, verified, and implemented have become an important part of the broader plastics policy conversation.
Why Is Mass Balance Used?
In many manufacturing systems, recycled and virgin raw materials are processed together within the same equipment and infrastructure. Separating these materials into entirely different production lines is not always practical or feasible. In many petrochemical and polymer manufacturing systems, materials are processed through large-scale, integrated infrastructure designed to optimize efficiency, product quality, and economics. Creating separate production systems for recycled and virgin feedstocks could require duplicative infrastructure and may not always be technically, operationally, or economically practical.
Mass balance accounting is designed to help track how much recycled material enters the system and how that recycled content is attributed to outputs produced from the process.
For example, a household may choose to pay for renewable electricity through their utility provider, even though the electricity moving through the grid comes from a shared energy system. The renewable energy purchased is accounted for within the broader system rather than delivered through a dedicated power line directly to the home.
Mass balance systems work similarly in some manufacturing environments where recycled and virgin materials are processed together within shared infrastructure.
What Mass Balance Does Not Do
Mass balance accounting does not physically trace individual recycled molecules into specific products. Instead, it provides a bookkeeping framework that tracks recycled inputs through a manufacturing system and allocates recycled-content claims according to established accounting rules. While approaches vary across certification systems and regulatory frameworks, mass balance is designed to ensure that recycled-content claims remain linked to the amount of recycled material entering the system and that total recycled-content claims do not exceed the amount of recycled material entering the system. In this way, mass balance serves as a material accounting framework rather than a physical tracing mechanism.
How Does It Work?
Imagine a manufacturing system that processes both virgin and recycled raw materials together. Under a mass balance approach, companies track:
how much recycled material enters the system
how materials move through production
and how recycled content is allocated to finished products
For example, if 100 tons of recycled feedstock and 900 tons of virgin feedstock enter a manufacturing system, the company may allocate recycled-content attributes to specific products according to the applicable accounting rules. However, it cannot claim more than 100 tons of recycled content across all products combined.
Are There Different Types of Mass Balance Systems?
Yes. Different systems may track and allocate recycled content in different ways depending on:
manufacturing infrastructure
supply chains
certification frameworks
and regulatory requirements
Different allocation methods can influence how recycled content is attributed to products, which is why they are often a focus of policy, certification, and stakeholder discussions.
Chain-of-Custody Approaches
These approaches describe how materials and associated sustainability characteristics are tracked through a supply chain. ISO 22095 identifies several chain-of-custody models used across industries, including recycled materials, forestry products, agriculture, textiles, and plastics
Segregated
Materials with specified characteristics (such as recycled content) are kept physically separate from other materials throughout the supply chain.
Controlled Blending
Materials with and without specified characteristics are physically mixed in defined proportions, with controls in place to ensure claims accurately reflect the composition of the resulting outputs.
Book-and-Claim
Specified characteristics are transferred through a certificate or accounting system rather than through direct physical tracking of materials.
Allocation Approaches
Once materials are tracked through a mass balance system, different methods may be used to assign recycled content or other specified characteristics to outputs. These approaches are often the subject of ongoing policy, certification, and industry discussions.
Proportional Allocation
Recycled content is assigned proportionally across eligible outputs based on the amount of recycled material entering the system.
Polymer-Only Allocation
Recycled content is allocated only to polymer outputs used to manufacture new plastic products.
Free Allocation
Recycled content may be allocated among eligible outputs within defined system rules rather than being distributed proportionally.
Fuel-Exempt Approaches
Certain frameworks exclude fuels or energy products from receiving recycled content attribution, while others treat these outputs differently depending on the applicable methodology or regulatory framework.
Different approaches can produce different accounting outcomes, which is one reason mass balance continues to be actively discussed among policymakers, researchers, certification systems, and industry stakeholders.
Why Is Mass Balance Debated?
Mass balance discussions often focus on:
how recycled content should be allocated
what outputs should qualify
how systems should be verified
and how recycled content claims should be communicated
Different accounting approaches can produce different outcomes depending on:
system boundaries
allocation methods
chain-of-custody rules
and how recycled inputs are assigned to final products
Many mass balance systems rely on third-party certification, auditing, documentation requirements, and chain-of-custody standards to verify material flows and support recycled-content claims, although specific requirements vary across frameworks and jurisdictions.
Some discussions center on whether mass balance accounting provides sufficient transparency and traceability for recycled-content claims. Some stakeholders prefer approaches that rely on physical segregation or direct traceability, while others view mass balance as a practical accounting solution for tracking material attributes through complex manufacturing systems.
Because of these differing approaches and perspectives, policymakers, companies, researchers, certification bodies, and sustainability organizations continue evaluating how mass balance systems should be defined, verified, and communicated.
Why Is It Relevant to Advanced Recycling?
Mass balance is often discussed in connection with advanced recycling because many advanced recycling outputs enter large manufacturing systems where materials are blended and processed together. In these systems, mass balance accounting may be used to help track recycled content through the broader production process.
An Evolving Conversation
As recycling technologies and circular economy systems continue evolving, discussions around mass balance are also evolving. Questions surrounding transparency, verification, accounting methods, and communication remain active areas of discussion among policymakers, researchers, manufacturers, and sustainability organizations.
Understanding what mass balance is, and what it is not, can help support more informed conversations about recycling systems, recycled content, material tracking, advanced recycling, and the broader role of accounting systems in supporting circular economy objectives.