Understanding the butterfly diagram

Rather than take the throughput approach of the linear economy, the circular economy has more of a ‘metabolistic’ approach, inspired by the model of a natural system. In it, materials circulate and cascade around the system, adding value at all levels and building a resilient overall system. The important thing to remember is that everything is designed to fit the system: this is an upstream, design-led initiative, rather than a downstream, reactive approach.

Look at the diagram below. It shows a big-picture view of how the circular economy works. There are 2 material cycles. Biological materials on the left, technical materials on the right. These two cycles look like the wings of a butterfly, which is why the diagram is often affectionately known as the Butterfly Diagram. Let’s explore them in turn.

Biological cycle

The biological cycle, as the name implies, contains natural materials such as food or cotton that can be safely and productively returned to the biosphere. All activity in the biological cycle is ultimately designed to regenerate the biosphere. Regenerating the biosphere means that we are constantly replenishing stocks for future cycles, whilst importantly drawing down carbon into the soil and preventing it from escaping into the atmosphere.

Technical cycle

The technical cycle works in a slightly different way. Here, materials and components that can’t be returned to the biosphere, such as metals and alloys, are kept within the cycle and circulated for as long as possible. The key here is to keep products,components and materials at their highest possible value at all times through repair, reuse, remanufacture and recycling. Think back to week 1 when we looked at the loss of embedded value in the linear economy. The fewer alterations that a product or component requires (processes which often require material and/or energy input), the greater the economic benefit and the lower the environmental impact.

Consume and use

A key distinction between the biological and technical cycle is the way in which we interact with materials: the biological cycle consumes, while the technical cycle uses. In the biological cycle, organic materials need to be gradually broken down, often in order to return to the soil. Without it the cycle doesn’t work: an apple is no use to the biocycle if it sits rotting in a box for instance. Conversely consumption isn’t great in the technical cycle if we’re going to focus on maintaining value, hence the focus on use. Materials in the system are there to be used, not used up.

Separate cycles

One of the important things about these two cycles is that they must be kept separate. Technical materials must not leak into the biological cycle and vice-versa. Many problems occur when this happens. For example, despite being fully recyclable, many plastics are unable to be recycled because they are contaminated with food or other waste from the biological cycle.

To sum up, the biological cycle is designed to regenerate the biosphere, while the technical cycle is designed to restore and maintain value. This is why we refer to the circular economy as a system which is restorative and regenerative by design.

Take a closer look at the butterfly diagram. How do you think economic value is created in each of the two cycles?