Cradle to cradle is a system boundary approach in Life Cycle Assessment that extends from raw material extraction (the cradle) through production, use, and end-of-life treatment, and then continues through the next product life cycle where materials are recovered and reused (returning to the cradle). This creates a closed-loop system boundary that accounts for the complete cycle of material flows across multiple product generations.
In contrast to traditional cradle-to-grave assessment, which terminates at final disposal, the cradle to cradle approach recognises that materials and components from end-of-life products can serve as inputs to new production cycles. This system boundary is particularly relevant when assessing products designed for circular economy principles, where materials maintain their utility through multiple life cycles rather than being disposed of as waste.
According to ISO 14040 principles, when defining the system boundary for a product system, the practitioner must clearly specify which life cycle stages are included. The cradle to cradle boundary encompasses all stages of the initial product life cycle plus the subsequent reprocessing and incorporation into new products. This requires careful modelling of recycling activities, material quality changes, and the displacement of virgin materials in subsequent production cycles.
When applying a cradle to cradle system boundary, it is essential to account for any quality degradation during reprocessing, as materials rarely maintain identical properties across multiple cycles. The assessment should include all energy and material inputs required for collection, sorting, and reprocessing of end-of-life materials, as well as any by-products or residual wastes from these activities.
This approach differs from cradle-to-gate assessments (which end at the factory gate), cradle-to-grave assessments (which end at final disposal), and gate-to-gate assessments (which cover only selected intermediate stages). The cradle to cradle boundary provides the most comprehensive view of material flows in circular systems and supports decision-making for sustainable product design.
