Using the metaphor of metabolism, durable materials are considered technical nutrients that can be recycled within technical metabolisms. A product designed to meet cradle-to-cradle design principles will be designed with a system for recovery and recycling as part of its business model. A product of service stands in contrast to a product of consumption in that it provides a service to the user but is not itself consumed. When the service is no longer provided, the product materials can be reused or recycled.