Mass balance

Mass balance is a chain-of-custody accounting model: certified input (recycled or bio-based feedstock) is mixed with conventional input in a shared system, and the certified quantity is allocated to specific outputs by bookkeeping, audited so claims never exceed inputs. ISO 22095 places it among the recognised models alongside identity preservation, segregation and book-and-claim.

Its legitimate home is chemical recycling and shared crackers, where physical segregation is impossible. Its risk is marketing inflation: "contains recycled material via mass balance" can describe a product with little or no recycled molecules in the specific item sold. The buyer's discipline is to ask which model backs a claim. For our physical trade — flake, pellet, sheet — content claims rest on segregation or controlled blending with batch-level declarations, and note that mass-balance allocation is not accepted for the UK Plastic Packaging Tax's 30% test.