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Model reuse, repair, and recycling as distinct pathways, then compare them against the same delivered service. Start by defining the decision, geography, time period, functional unit, and supply-chain boundary; map product and material stocks and flows; and quantify physical, environmental, and cost outcomes with methods suited to each question. A circularity score alone cannot show whether an intervention reduces environmental impacts.
What decision is the model meant to support?
Be specific about the choice being compared and who will use the result. A model might assess packaging rotations, a repair program, product take-back, use of recovered material, or a redesign of the reverse-logistics network. The decision determines which flows, costs, and outcomes matter.
Set the geography, period, organizations or supply-chain stages covered, and the decision-maker’s role. Where relevant, make ownership, take-back responsibility, return incentives, reverse-logistics arrangements, and responsibility for repair or recovery costs explicit. These details can change participation, costs, and the flows the model needs to represent.
How do you make scenarios comparable?
Define the functional unit as the service delivered, with its quantity, quality, and duration. For example, a packaging comparison could be framed around a specified number of successful deliveries; a durable-product comparison could use a defined service over a stated number of years. The unit should reflect what the buyer or user actually needs, not simply the number of products manufactured.
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Normalize every scenario to that same service. Comparing one new product with an unspecified number of repaired or reused products can conceal differences in service life, failure, or performance. If scenarios deliver different amounts or quality of service, adjust the reference flows or report the difference rather than treating them as equivalent.
The EU Product Environmental Footprint (PEF) Recommendation is one specific life-cycle methodology. It calls for reuse and refurbishment to be represented in the reference flow and full life-cycle model. Treat that as guidance within the PEF method, not as the only permissible LCA approach.
What belongs inside the supply-chain boundary?
Draw the boundary before calculating results. Include the stages needed to deliver the defined service and follow products and materials through their relevant lives. Depending on the decision, the model may cover acquisition, design and production, distribution, use, collection, reverse transport, inspection and sorting, repair or refurbishment, reuse, recycling, and residual treatment. State cutoffs and excluded stages, and apply the same boundary to each scenario.
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ISO 59020:2024, Circular economy — Measuring and assessing circularity performance, sets out guidance for measuring and assessing an organization’s circularity performance within defined economic systems. Its boundary and indicator framework can inform the model, but circularity measurement does not replace scenario-specific life-cycle assessment. ISO’s standard page describes the standard, published in May 2024.
How do you map stocks and flows?
Build a physical flow map for the chosen period and geography. Track products, components, and materials through the forward chain and back through collection and recovery. Include stocks as well as flows: inventory in use, items awaiting inspection, work in repair, recovered feedstock, and material that leaves the system can all affect the balance.
Record quantities by product or material where practical, along with losses, quality grades, destinations, and the data source. Separate collected material from material actually recovered, and recovered material from material that reaches a useful next application. A mass balance helps expose unaccounted losses, but it does not by itself establish environmental benefit or economic value.
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- Identify data owners and whether inputs are measured, estimated, or assumed.
- Record the data year, geography, units, and applicable product or material grades.
- Keep process losses and residual disposal visible rather than folding them into a single recovery figure.
How should each circular pathway be represented?
Reuse: count rotations and account for returns
Specify how many uses an item completes, whether the first use is included in the reported count, and how many subsequent reuses occur. The EU PEF Recommendation defines reuse rate in terms of the number of times a material is used. Make the denominator explicit: a percentage based on total uses is not interchangeable with one based only on subsequent reuses.
Model the processes that make each rotation possible, such as return collection, inspection, cleaning, maintenance, and redistribution. Account for return rates, breakage, and items rejected before another use, then include the item’s eventual end of life. Reuse can require different packaging, transport, or cleaning inputs; include those where they fall within the boundary.
Repair and refurbishment: model the life extension
Represent the repair or refurbishment process, including replacement parts and relevant labor, energy, and material inputs. Estimate failure and repair frequency, repair success, and the additional service life achieved. Compare that service with the replacement scenario on the same functional unit.
Product characteristics can affect whether repair is feasible and whether components remain in use or can be recovered. Durability, maintenance, repairability, software updates or upgrades, disassembly, and separability may matter. IEC TS 63428:2024 addresses material circularity in electrotechnical product design; its scope excludes economic, social, and energy aspects, so do not treat it as a universal definition of circularity. A repair pathway should not be assumed to have lower impact without evidence from the scenario model.
Recycling: follow material through recovery and its next use
Represent collection, sorting, processing, process yield, and the quality of recovered material. Then identify its actual destination and the material or product it can replace, if any. Collection alone is not recycling, and recovered mass does not show what level of virgin production is displaced.
State the allocation or crediting convention used to handle recycling and the next product system. Test consequential assumptions—especially the amount and quality of virgin material displaced—as sensitivity cases. The EU PEF Recommendation includes circular-footprint treatment for waste; use its rules when applying that methodology rather than implying that one crediting convention fits every LCA.
Which methods answer which questions?
Use complementary methods without blending their outputs into one unexplained measure. Material flow analysis (MFA) answers where products, components, and materials go within a system defined in space and time. Life-cycle assessment (LCA) evaluates environmental impacts across the life cycle for the defined function. Material flow cost accounting (MFCA) links physical flows to associated costs, including costs of material and energy losses.
| Method or framework | Question it helps answer | Useful output | What it does not establish by itself |
|---|---|---|---|
| Material flow analysis (MFA) | Where do stocks and flows of products, components, or materials go within the defined system? | Quantity or mass balances, stocks, losses, and destinations. | Full life-cycle environmental impacts or costs. |
| Life-cycle assessment (LCA) | What environmental impacts arise across life-cycle stages for the defined function? | Impacts across selected categories and stages. | A result independent of the functional unit, boundary, data, allocation choices, or impact method. |
| Material flow cost accounting (MFCA) | Where do material and energy losses occur, and what costs are associated with the flows? | Physical flows and their associated costs. | An environmental impact assessment. |
| ISO 59020 circularity measurement | How should an organization define and assess circularity performance with indicators? | A structured approach to boundaries and indicator selection. | A complete LCA result or proof that an intervention improves environmental performance. |
| NIST production-in-a-circular-economy model | How can production and closed-loop recovery activities be mapped? | A reference activity model that includes recovery and R-strategies. | Case-specific performance data. |
ISO describes MFCA as tracing material flows and stocks, quantifying them in physical units, and evaluating costs associated with material flows and energy use. Its ISO 14052:2017 page says the edition was reviewed and confirmed current in 2022; check its status if currentness matters for a formal application. ISO 14052:2017 also concerns MFCA implementation in supply chains.
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NIST’s Production in a Circular Economy resource describes a CLR Activity Model for material-recovery activities and R-strategies including reuse, repair, remanufacturing, and recycling. It is a reference model, not a source of performance assumptions for a particular chain. NIST’s circular-economy manufacturing models provide the model description.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What should you compare and test?
Report separate physical, environmental, and economic results. At minimum, select measures relevant to the decision across virgin-material demand, useful life or rotations, recovery yield and quality, and whole-life environmental impacts. Include cost when the decision concerns economics. If using circularity indicators, disclose each formula, denominator, system level, and data basis; no universally valid single weighted score is established by these cited methods.
Test assumptions that could change the preferred option. Vary rotation count, return rates, repair success and life extension, recycling yield and recovered-material quality, transport distance, energy mix, and substitution assumptions where they are material. Check for burden shifting between life-cycle stages, geographies, or environmental impact categories. A result that improves one indicator may worsen another.
How should you report the model?
Make it possible for a reader to understand what the result covers and how it was produced. Distinguish measured values from assumptions, and document data year, geography, primary or secondary data status, allocation choices, exclusions, and model level. Show scenario inputs and outcomes alongside the functional unit and boundary so that differences can be interpreted rather than attributed to the pathway label alone.
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Standards and government models provide methods, not universal performance rates for reuse, repair, or recycling. Use case-specific evidence for numerical assumptions and state its source, year, geography, and boundary. Avoid presenting a circularity indicator as a substitute for environmental impact results or a favorable pathway as an established benefit without scenario evidence.
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