ENStarting point
A life cycle assessment should compare systems that fulfil the defined function and use consistent boundaries, data and calculation rules. An emissions result per kilogram of resin does not automatically represent the product's impact or an environmental advantage across all categories.
Define the decision the study needs to support
A study may assess a raw material substitution, compare treatment pathways or support the development of a component. These questions involve different systems and results. Specify who will use the analysis, which alternatives are available and what decision will be made. The purpose determines the depth, data requirements and way the conclusion is communicated.
In its publicly available scope, ISO 14044 lists elements such as goal and scope, inventory, impact assessment, interpretation, reporting and critical review. [1] The study description should explain how these elements will be addressed. A preliminary estimate for selecting design assumptions can be useful, provided it is not presented as a definitive comparison or a completed comprehensive assessment.
Compare function, not just purchased mass
One kilogram of resin may serve as a reference unit when comparing equivalent materials, but a product decision requires checking the service delivered. If an alternative requires more mass, changes service life or generates more scrap, the result per kilogram may not represent the result per functional part. Define the relevant performance, duration and conditions of use.
The quantity of each material required to fulfil the function must be supported by engineering and testing. Do not assume equivalence simply because two resins belong to the same family. Record which requirements have been demonstrated and which remain assumptions. If the function is not comparable, present separate scenarios and explain the difference, instead of producing a ranking that suggests direct substitution where none exists.
Set boundaries and maintain a consistent approach
Identify collection, transport, sorting, washing, conversion, additives, losses, energy, treatment of secondary streams and other relevant stages. A cradle-to-gate comparison of resin does not automatically cover part manufacturing, use and end of life. The title and conclusion should reflect the stages actually modelled.
For a waste management comparison, the function may be to treat a given quantity of waste, including associated products and services in line with the chosen methodology. For a resin comparison, the function and boundary will be different. The JRC report on recycling pathways shows the importance of considering recovery, processing impacts, the specific characteristics of the stream and feasibility. Its results apply to the scenarios studied and do not replace data from a Brazilian operation. [2]
Build an inventory with traceability and representativeness
Give preference to operational measurements when they are appropriate to the question. Match consumption and production over the same period and reconcile inventories. Separate pilot campaign data from routine operating data. For secondary information, record the database used, version, location, technology and year. A spreadsheet must enable another person to reconstruct the source of each relevant input.
Assess geographical and technological representativeness. Distances, the electricity mix, yield and waste treatment may differ between the available reference and the facility being analysed. Where data are unavailable, state the assumption and its rationale. Prioritise further collection for parameters that could reverse the decision; there is no need to refine every number equally if only a few dominate uncertainty in the result.
Explain allocation and credits without double counting
An operation may produce several fractions and provide a treatment service. The distribution of burdens and consideration of the substitution of other materials must follow the approach selected for the study. Record how incoming waste, products, co-products and end of life were treated. Avoid combining rules from different databases merely because each favours an alternative.
Where a benefit from substitution is modelled, specify which product would be replaced, in what quantity and with what equivalent quality. Do not assume one kilogram replaces another without analysing function. Also check whether the same benefit has been counted at two stages of the same system. If a methodological choice strongly affects the comparison, present a sensitivity analysis showing its influence.
Run an illustrative calculation with clear limitations
An entirely hypothetical example, restricted to emissions associated with the quantity of resin used: alternative A uses 1.00 kg per part and a factor of 3.00 kg CO₂e/kg. Alternative B uses 1.15 kg per part and a factor of 1.50 kg CO₂e/kg. Assuming functional equivalence has already been demonstrated and the factors have compatible boundaries, the results are 3.00 and 1.725 kg CO₂e per part, respectively.
The relative difference is (3.00 − 1.725) ÷ 3.00 = 42.5%. It is not 50%, because the masses differ. This calculation does not represent a complete LCA or actual factors for any resin. Conversion, scrap, use and end of life have been excluded from the example. The conclusion could only be broadened after including the stages relevant to the objective and checking the other assumptions.
Visual explanation · hypothetical example
Compare on the same functional basis
Emissions associated only with the resin quantity per part. Functional equivalence and compatible boundaries are assumptions of this example.
- Alternative A
- 3.00 kg CO₂e/part
- Alternative B
- 1.725 kg CO₂e/part
Common scale: 0 to 3.00 kg CO₂e per part.
This limited calculation is neither a complete LCA nor actual factors for any resin.
View the example's data and calculations
| Alternative | Mass per part | Illustrative factor | Result |
|---|---|---|---|
| A | 1.00 kg | 3.00 kg CO₂e/kg | 3.00 kg CO₂e/part |
| B | 1.15 kg | 1.50 kg CO₂e/kg | 1.725 kg CO₂e/part |
Test sensitivity and other impact categories
Vary critical parameters within justified ranges: yield, distance, part mass, energy consumption or service life. Identify the point at which the conclusion changes. An alternative that shows an advantage only under an optimistic assumption calls for a different investigation from one whose result remains stable under plausible conditions. Show ranges and scenarios without suggesting precision the data cannot support.
An advantage in climate change impact does not demonstrate an advantage across all environmental categories. The assessment should address impacts relevant to the objective and acknowledge possible trade-offs between them. ISO 14040 sets out the principles and framework of LCA; its publicly available scope does not replace methodological development or consultation of the relevant standards in full. [3] In the presentation, distinguish the climate footprint, other categories and the overall conclusion.
Communicate a conclusion proportionate to the evidence
The report should make it possible to identify alternatives, function, boundaries, data, assumptions, limitations and results. Define a review appropriate to the intended purpose, particularly when a comparison will be used externally. Do not turn a favourable internal scenario into a broad public claim without checking the applicable methodological and communication requirements.
The article on environmental claims complements this stage. For the circularity decision, the analysis should show what explains the difference and which data could still change it. A well-structured LCA helps improve the design, select measurements and support a clearly bounded comparison, keeping the conclusion as specific as the available evidence.
Sources and references
References accessed on 5 October 2026. The numbering in the text indicates the concepts supported by each source.
References to ISO standards use their publicly available scopes; full requirements should be consulted in the respective standards.
- ISO 14044:2006 — Environmental management: life cycle assessment, requirements and guidelines. Publicly available scope and identification of the 2017 and 2020 amendments.
- Garcia-Gutierrez, P. et al. Environmental and economic assessment of plastic waste recycling. European Commission, JRC132067, 2023.
- ISO 14040:2006 — Environmental management: life cycle assessment, principles and framework. Publicly available scope of the standard.
Circuvia corporate content to support project discussions. Methods, acceptance criteria and applicable requirements are defined within the scope of each operation.
