Plastic Accounting: Measure the Flow, Not Just the Waste

Most companies can tell you how much packaging they bought. Far fewer can tell you where that plastic actually went. That gap is the whole point of plastic accounting — and it is where credibility is won or lost.

Follow the material, not the invoice

Plastic accounting follows material flows across the value chain: inputs, products placed on the market, reuse, recycling, disposal and losses. A WBCSD review found that existing disclosure initiatives did not consistently require reporting of both inputs and outputs. So if your account stops at "packaging purchased," you are describing a purchase, not a flow. Ask yourself: can I trace a tonne of plastic from the moment it enters my operations to where it ends up?

Define the boundary before you calculate

Before any number is produced, specify the entity, sites, products, plastic types, life-cycle stages, geography, reporting period and treatment of value-chain data. Methods vary, so disclose the method you chose and any exclusions. This is not bureaucracy — it is what makes two numbers comparable at all.

Keep mass-flow accounts separate from impact estimates

Tonnes of plastic used, waste generated and leakage estimated are three different indicators. Leakage is typically modelled from sources and pathways; it is not the same as directly observed pollution. The Plastic Leak Project methodology was developed to map, measure and forecast leakage across value chains. Label each figure for what it is.

Show your calculation trail

Retain source data, units, conversion factors, assumptions, allocation rules and evidence for reported quantities. Identify whether values are measured, supplier-reported or modelled, and explain uncertainty and estimation changes. These are practical controls for making estimates reproducible. The WBCSD review describes a landscape of different measurement and disclosure approaches — not one universal method.

• State the basis for any recycling or diversion claim, and report the quantities and destinations used in the account.
• Do not equate a recycling claim with verified material fate.
• Remember: the available sources do not establish a single mandatory corporate plastics-accounting standard.

Hong Kong reporting: availability is not obligation

HKFRS S1 and S2 are effective from 1 August 2025, but HKICPA says their use remains voluntary unless regulators or legislation require it. Hong Kong's roadmap envisages phased adoption for large publicly accountable entities, with full adoption no later than 2028. Under HKFRS S1/IFRS S1, disclose material sustainability-related risks and opportunities that could reasonably affect prospects — cash flows, access to finance or cost of capital — over the short, medium or long term. Plastic metrics are not automatically required just because they can be measured. And avoid presenting plastic impacts as a prescribed HKFRS S2 metric: S2 is the climate-related disclosure standard, and plastic-use and leakage accounting is not identified in the cited material as a dedicated disclosure standard.

Where valuation comes in

IVS, effective 31 January 2025, says significant ESG factors should be considered in determining value, and lists waste management and resource scarcity or efficiency among environmental factors, calling for professional judgement to the extent factors are measurable and reasonable. Connect plastic exposure to valuation only through supportable inputs: test whether plastic regulation, waste costs, resource constraints, remediation or market effects influence cash flows, risk or other assumptions, and document the evidence. IVS provides the framework, not a plastic-specific formula.

Treat the treaty as unsettled

UNEA resolution 5/14 was adopted in February 2022 by members from 175 countries, launching negotiations for an international legally binding instrument on plastic pollution. INC-5.2 took place 5–15 August 2025 in Geneva and ended without consensus; the process remained active, with further negotiations anticipated in early 2026. Do not report proposed provisions as agreed law.

For a deeper mathematical treatment, see Plastic Accounting in Practice: A Mathematics Guide for Sustainability Professionals. For the policy context, see the INC-5.2 analysis, the IVS standards, the WBCSD plastic disclosure review, and HKICPA's FAQs on HKFRS Sustainability Disclosure Standards.