In their book Cradle to cradle, remaking the way we make things (2002), Michael Braungart and William McDonough called for a radical change in industry: a switch from a cradle-to-grave pattern to a cradle-to-cradle (C2C) pattern.

Taking a counter intuitive approach to the 3R strategy (Reduce Reuse Recycle), the concept strives to rethink the notion of recycling, as most of the traditional recycling activities are actually “downcycling” (i.e.: waste materials or useless products are converted into new materials or products of lesser quality and reduced functionality) instead of “upcycling”, where old products are given more value not less. To do so, the authors introduce the notions of biological nutrients and technical nutrients, notions often used in circular economy literature. Biological nutrients are materials that can safely re-enter the environment. Technical nutrients on the other hand are materials that should remain within closed-loop industrial cycles.  By designing products that can distinguish the two types of nutrients, C2C aims to close the loop of industries, technical nutrients being reused indefinitely without quality loss, while biological nutrients being able to restore soil quality.

Cradle to cradle departs from the general agreement around eco-efficiency. According to Braungart, most recycling is downcycling, which limits usability of materials and maintains the linear, cradle-to-grave dynamic of the material flow system (Braungart, McDonough and Bollinger, 2007).  In contrast to eco-efficiency, eco-effectiveness proposes the transformation of products and their associated material flows so that they form a supportive relationship with ecological systems while ensuring future economic growth. The goal, state the authors, is not to reduce waste production anymore, as the very notion of waste disappears in favour or resources and materials constantly circulating. If eco-efficiency measures look at strategies such as volume minimization, design for repair and durability, eco-effective approaches pay less attention to these factors, providing materials constantly maintain their status of productive resources over their multiple life cycles. The goal of eco-effective strategies is to generate cyclical, cradle-to-cradle ‘‘metabolisms’’ that enable materials to maintain their status as resources through upcycling.

C2C design principles rely on three principles: Waste is food, rely on renewable energy sources, and celebrate diversity. By getting inspired from natural ecosystems, the ultimate goal of the Cradle to Cradle approach is to eliminate the amount of waste resulting from industrial and commercial processes. The three principles are described below:

Waste is food

The perceived limitations of Eco-efficiency pushed Braungart and McDonough to define further the approach developed within the cradle to cradle framework to design products and industrial processes that turn materials into nutrients by enabling their perpetual flow within one of two distinct metabolisms: the biological metabolism and the technical metabolism. Here, the concept of waste is eliminated for the profit of nutrients. In the biological metabolism, biological nutrients are biodegradable materials (natural/plant-based materials). They are products of consumption, as they can be ‘consumed’ in their life cycle (through physical degradation or abrasion). At the end of their life, they can safely return to be used as input for living systems. On the other hand, a technical nutrient is a material (synthetic or mineral) that has the potential to remain safely in a closed-loop system of manufacture, recovery, and reuse, while maintaining its highest value through many product life cycles. As in the concept of industrial ecology, the effective management of these two distinct nutrient flows associated with the biological and technical metabolism necessitates the formation of collaborative business structures with the role of coordinating the flow of materials and information throughout the product life cycle (Braungart and McDonough, 2007). One management approach favoured by the authors is intelligent materials pooling, which allows companies to pool material resources, specialized knowledge and purchasing power relating to the acquisition, transformation and sale of technical nutrients and their associated products.

Use renewable energy

Living organisms thrive thanks to solar energy. As this energy can be considered to be an eternal overabundant energy source, In the Cradle to cradle framework, McDonough and Braungart promote the use of this renewable energy source for heating, electricity and day lighting within buildings and for manufacturing processes within the industry. Other sources or renewables (geothermal, wind, hydro or biomass energy) should also be widely used. The use of renewable energy as such is an accepted broadening of the second Cradle to Cradle principle. Based on its vision of being entirely supplied by solar energy, Cradle to Cradle design is not limited by any constraints on the energy use during the life cycle of a product. As long as the energy quality meets the requirements (current solar income) the energy quantity is irrelevant.

Celebrate diversity

C2C departs from the “one size fits all” type of solutions and, inspired by nature’s diversity, encourages to value diversity of species, cultures, and solutions. The framework focuses on using local surroundings to develop tailored solutions adapted to the challenges of the locations.

If the concept of C2C has gained lots of interest among large businesses (Nike, Desso, Shell among others), it is however regarded with a certain degree of scepticism in the academic environment. LCA practitioners have claimed that it does not include all life cycle stages and therefore cannot be considered a serious concept for sustainable design. Danish researchers Anders Bjørn and Maria Strandesen have summarized other inherent critical points of the concept, synthetized below.  One first critic is that absolute closed loop recycling as advocated by Braungart and McDonough are in fact not always possible. Thermodynamically, it has been shown that the work required to separate ideal mixtures of two or more substances increases without bounds as the separation process proceeds .Thus the last bit of impurity of one substance diluted in another substance requires infinite amounts of energy to separate (Gutowski, 2008). In some cases, impurities can only be removed down to a certain level in current during the recycling processes. Some impurities may persist in low concentrations in the recycled materials. Therefore while it may be useful to separate biological from technical nutrient, this alone does not guarantee closed loop recycling. Second critic, according to Bjørn and Strandesen, the addition of biological nutrients to the environment will not necessarily result in a benefit unless the specific ecosystem has been degraded by human impacts as a starting point. First, many materials that qualify as biological nutrients do not in fact contain any macro- or micronutrients, making it pointless to be returned to the soil.  The C2C principles do not take into account the level of concentration of nutrients brought back to the soil and some species might react differently according to the new input. This ecosystem manipulation might in some cases have some negative consequences. Finally, it is also pointed out that even if the C2C principles are fully applied in society, as long as our economic approach is based on constant growth, we will still experience resource scarcity and loss of biodiversity. As history shows that direct material consumption (DMC) per person is well correlated with the income and thus with economic growth, this means that even though 100% closed loop recycling is to be achieved it does not eliminate the need for virgin resources nor the problem of resource scarcity.

The sometimes dogmatic Cradle to cradle framework, despites its critics, bring along key principles that form a strong foundation for a circular economy. The distinction between technical and biological nutrients as key elements of a closed loop model, the reliance on renewable energies and diversity as a condition for resilience are three key principles found in the various attempts trying to define a circular economy. The principles are applied at product level or company level but also help shaping the way organisations can interact at territorial level.