3 Process Emissions Missing From Product Carbon Footprint Reports

A product carbon footprint report can look complete on paper. Materials are mapped, supplier data is collected, transport is accounted for, and yet the final footprint can still be incomplete when manufacturing activities are not fully captured in the calculation.

This is an important consideration in product carbon footprint (PCF) work. Teams collect supplier data and build out a bill of materials (BOM), then apply relevant emission factors to the materials and components included in the calculation. It can feel thorough. But a BOM tells you what materials and components make up a product, not everything required to turn those inputs into a finished unit. The electricity used by a molding machine, the steam used in a coating process, and material lost through scrap may require additional production data and calculation steps.

Below are three process-related emission sources that can be missed in product carbon footprint reports, why they may be overlooked, and how to bring them into the PCF boundary.

Manufacturing can generate greenhouse gas emissions from several different sources. Some are direct emissions from fuel combustion or industrial processes, while others are indirect emissions associated with purchased electricity, steam, or heat. These sources are classified differently under the GHG Protocol.

Fuel burned directly on site, in an oven, furnace, or boiler, generally falls under Scope 1 when the equipment or facility is owned or controlled by the manufacturer. Purchased electricity, steam, heat, or cooling used in manufacturing generally falls under Scope 2. The emissions occur at the energy-generating source, but are accounted for by the organization consuming the purchased energy.

A product carbon footprint can include emissions associated with these manufacturing activities when they fall within the defined PCF system boundary. It can also include emissions associated with purchased materials and components, which may correspond to upstream Scope 3 emissions in a corporate GHG inventory.

The production stage can therefore contain more than the materials listed in a bill of materials. Process electricity, production utilities such as heat, steam, and compressed air, and production losses such as scrap, yield loss, and rework can all affect the emissions attributable to a finished product.

The key point is simple: a BOM describes the materials and components in a product, but it does not by itself describe the energy and production inputs required to manufacture that product.

A bill of materials is built to answer a procurement question: what parts and quantities go into this product? It was not designed to answer a manufacturing question: what energy and material inputs were required to produce this unit?

Under ISO 14067, the international standard for quantifying and reporting a product carbon footprint, the study must define its system boundary and account for the relevant life-cycle stages within that boundary, whether the study covers a partial life cycle such as cradle-to-gate or a broader life cycle such as cradle-to-grave. The manufacturing stage can include its own inputs, such as purchased electricity, fuel, steam, compressed air, and materials and energy associated with production losses. These are generally not BOM items in the traditional sense. They are production inputs tied to how a product is manufactured rather than simply what it is made of.

When a PCF calculation relies only on material-level data, it can omit relevant emissions associated with manufacturing activities. Depending on the source and accounting treatment, these can include direct emissions from fuel combustion and indirect emissions associated with purchased electricity, steam, or heat. If those manufacturing inputs fall within the defined PCF system boundary but are not included in the calculation, the resulting footprint does not fully represent the emissions associated with that boundary.

The gap is therefore not necessarily a problem with the BOM itself. It is a limitation of using the BOM as the primary source for a calculation that also needs to account for the production process.

Every unit that gets molded, machined, welded, or assembled requires energy to manufacture, and the associated electricity emissions depend on the electricity source and accounting approach.

For a manufacturer's corporate GHG inventory, purchased electricity is generally Scope 2. The emissions occur at the electricity-generating source rather than at the manufacturer's facility. In a PCF, the relevant electricity consumption can be attributed to the product when the manufacturing stage is within the defined system boundary.

The challenge is that process electricity is often recorded at the plant level, such as on a utility bill, rather than as a BOM line item. A BOM-based calculation therefore needs additional production data to determine how much electricity should be attributed to a specific product.

Determine the electricity used per unit produced, in kilowatt-hours per unit, and apply an appropriate emission factor based on the manufacturing location, electricity procurement method, or other applicable accounting approach. Include the resulting emissions in the production stage of the PCF, separate from the material-level emissions already accounted for.

For example, if an injection molding machine consumes a known amount of electricity per hour and produces a known number of units per hour under the relevant operating conditions, the electricity consumption can be allocated on a per-unit basis and combined with the appropriate electricity emission factor.

Beyond electricity, many manufacturing processes use additional energy and utility inputs that are generally not represented as BOM line items: heat from ovens or furnaces, steam used for processes such as curing or sterilizing, and compressed air used to operate pneumatic equipment.

These utilities can be difficult to attribute to a specific product because they may be shared across an entire production line or facility. A boiler generating steam for three different product lines, for example, does not automatically provide a product-level breakdown. Without an appropriate allocation or measurement method, the associated emissions may remain unallocated or be excluded from the product calculation.

Quantify the process energy and utilities consumed to manufacture the product, then apply the relevant emission factors. This can include fuel combusted in ovens or boilers, purchased or generated steam, and electricity used to generate compressed air. Allocate the relevant share to the product's production stage using a defensible method, such as production time, output volume, measured energy consumption, or another method appropriate to the process and available data.

The third gap is one that manufacturing teams understand intuitively but can be overlooked in product carbon footprint calculations: not every unit of material or energy that enters a process ends up in a shipped product.

Scrap is trimmed or discarded. Some units fail quality checks and require rework, consuming additional energy and potentially additional material. Yield loss means more raw material may need to be processed than the quantity ultimately shipped. A PCF calculation that uses BOM quantities without accounting for production losses can therefore assume an input-to-output relationship that does not reflect actual production.

Account for the material and process energy required to produce the shipped quantity, including relevant losses and any additional processing from rework, rather than accounting only for the material contained in the final product. For example, if 1.15 kilograms of material must be processed to yield 1 kilogram of saleable product, the footprint should account for the 1.15 kilograms processed and the associated production energy, provided those inputs fall within the defined system boundary and are treated consistently with the chosen allocation method.

A BOM provides an important foundation for a product carbon footprint, but it does not necessarily capture the energy, utilities, and production losses associated with manufacturing. A process-inclusive approach adds relevant production data so the manufacturing stage can be accounted for within the defined PCF system boundary.

* Depending on the defined PCF system boundary and available data.

The difference is not that a BOM-based approach is inherently incorrect. The limitation is that the BOM primarily describes the materials and components that make up the product. Production data is needed to account for the energy and material inputs required to manufacture the finished unit.

A process-inclusive PCF therefore connects what the product is made of with what it takes to manufacture it. The result is a more complete representation of the emissions associated with the defined system boundary.

An incomplete product carbon footprint is not just an accuracy issue. It can also affect the credibility and usefulness of the result. ISO 14067 emphasizes defining the system boundary and documenting relevant methodological choices and assumptions. If process electricity, utilities, or production losses are excluded from a PCF, that exclusion should be consistent with the defined system boundary and transparently documented. Otherwise, a customer, auditor, or procurement team reviewing the footprint may question how the reported figure was calculated.

There is also a practical consideration. Manufacturing data can reveal opportunities to reduce emissions and material use. A facility that measures electricity intensity can evaluate equipment efficiency or electricity sourcing. A team that quantifies yield loss can identify production steps associated with material waste and additional processing. When relevant manufacturing inputs are not reflected in the product carbon footprint, the calculation provides less information about which production activities contribute to the result and where improvements may have the greatest potential impact.

Consider two manufacturers making a functionally identical product from the same purchased materials. One uses more energy-intensive equipment and has a higher scrap rate. The other uses more efficient equipment, has a different electricity supply, and achieves a higher production yield. If both companies calculate their product carbon footprint using only the same material inputs and emission factors, their reported material-related footprints could be similar even though their manufacturing processes differ. When relevant production electricity, utilities, and losses are incorporated, the footprints can reflect those manufacturing differences.

For manufacturers responding to PCF requests from customers further down the value chain, this distinction can matter beyond their own reporting. Emissions associated with a supplier's manufacturing activities can form part of the customer's upstream product footprint, depending on the customer's system boundary and methodology. If relevant production data is missing from the supplier's PCF, the customer may also lack information needed for its own product-level calculation.

A process-inclusive PCF therefore does more than produce a number. It provides a clearer picture of the materials and manufacturing activities that contribute to that number, while making the underlying boundary, data, and assumptions easier to understand and review.

Closing these gaps does not necessarily require rebuilding your entire carbon accounting process from scratch. It requires treating production as a distinct part of the PCF calculation rather than relying on the BOM alone.

In practice, that means:

This does not necessarily require perfect data on day one. A reasonable estimate for process electricity per unit, clearly documented as an estimate and supported by an appropriate methodology, can be more useful than a footprint that excludes relevant production energy without explanation. The objective is to define and apply a PCF system boundary consistently, using the best available data and transparently documenting limitations and assumptions.

This is also where the right tooling can help. Carbalyze's platform, built around its AI assistant Caly, is designed to turn a bill of materials into a product carbon footprint aligned with the GHG Protocol and ISO 14067. Caly maps BOM materials to emission factors and produces a material-level PCF. Process electricity, utilities, and production losses still need production data added to the calculation, as described above.

Whether your production-related emissions are associated with a molding press or steam system, or your production losses include a scrap rate that has not yet been formally measured, the approach starts the same way: define the production boundary explicitly, quantify the relevant inputs and losses, and avoid treating the BOM as the entire footprint.

A product carbon footprint depends in part on the system boundary defined for the calculation. Material and supplier data can be comprehensive, yet the reported footprint may still be incomplete if relevant process electricity, utilities, and production losses within the defined system boundary are not included in the calculation. These gaps can be harder to identify than a line item on a BOM because they depend on production data, utility consumption, and manufacturing losses.

Accounting for relevant production inputs within the defined system boundary can provide a more complete representation of the manufacturing stage in a product carbon footprint.