What is the difference between mass balance and segregated chain of custody for low-carbon materials?
Segregation keeps certified or low-carbon material physically apart from ordinary material, so what you receive actually contains it. Mass balance lets the two mix and tracks the certified share on paper, so the low-carbon volume you sell never exceeds what went in over a period. The physical link is weaker, but the volumes still reconcile.
The five models in ISO 22095
- Identity preserved: material from one known source kept separate all the way. Strongest claim, highest cost.
- Segregated: certified material from several sources may be combined, but never with uncertified material.
- Controlled blending: certified and uncertified material mix in a known proportion, and that proportion is passed on with each batch.
- Mass balance: material mixes freely; certified quantities are tracked in an account, and outputs are allocated certified status up to the amount that went in.
- Book and claim: no physical link at all; certificates are traded separately from the material.
What each lets you claim
With segregation, a buyer can say the product contains the low-carbon or recycled material. With mass balance, the honest claim is that an equal quantity of certified input was bought and allocated to this product; any given batch may contain more or less of it. Claims should name the model used.
Where you meet each in practice
- Plastics and chemicals: recycled or bio-based feedstock often runs through shared crackers and reactors, so mass balance is common.
- Steel and aluminium: scrap and primary metal are usually melted together; some producers sell a mass-balanced share of an emission cut as low-carbon steel.
- Textiles: organic or recycled fibre can be segregated by lot, but blends often move to controlled blending or mass balance.
What to check before relying on a mass balance claim
- Which scheme certifies it, and is the site certificate valid for your supplier.
- The balancing period and the allocation rules, such as whether losses in conversion are deducted.
- Whether your buyer's product footprint rules accept an allocated figure in place of the physical average. Many product carbon footprint rules treat mass-balanced emission reductions cautiously, so confirm before using it in a footprint you publish.
- That the same certified quantity is not also sold as a separate certificate.
Worked example: recycled resin in a moulding plant
- Inputs in one balancing period: 300 t recycled resin, 700 t virgin resin, all mixed
- Conversion yield: 95%, so total output 1,000 x 0.95 = 950 t
- Mass balance: 300 x 0.95 = 285 t of output may be sold as recycled; each batch physically holds about 30%
- Segregated: only output from the line fed solely with recycled resin, again up to 285 t, may carry the claim, and it physically contains it
What Senseible does here
Senseible does not run chain-of-custody certification or keep mass balance accounts. It keeps the purchase invoices for certified and ordinary inputs in a supplier evidence trail, which a certifier or buyer can check against your volume records.
Sources: ISO 22095:2020, Chain of custody: general terminology and models
Last reviewed 2026-10-15.