Why Circularity is Not Enough

by Elias Stahl

This is a time of bold experimentation.

It may have taken a global crisis, but in some heartening ways we are rising to the challenge of building a more sustainable form of production and consumption.

The shoe industry is emblematic of what’s wrong with the status quo. 24 billion shoes are made every year, and one in five go straight to the landfill. Only 5% are recycled at end of life. As a major part of an industry responsible for 10% of global carbon emissions and 20% of global water pollution, there is a long way to go.

Three years ago, HILOS set out to develop an on-demand, circular supply chain for shoes – one that could have a global impact, eliminate overproduction and material waste, and ensure that every product could be disassembled and recycled.

3D printing is at the heart of that effort, translating digital files into parts printed on-demand with very high material efficiency. Until just a few years ago, the hardware, software, and materials didn’t exist for 3D printing to reinvent how we make shoes. Thanks to the investment of material companies like BASF and hardware companies like HP and AMT, startups like ours can now create new types of 3D-printed consumer products.

After engineering a radically new way to make shoes and launching these styles into market, HILOS began working with established brands to enable them to launch their own 3D-printed footwear lines. Our first collaboration launched into market last October, and since then, the pace of brand collaborations has rapidly accelerated. With such fast growth, we saw a need to take a step back and survey the impact of our current technology to better understand what we’ve built and where we can improve.


  • Key findings
  • CO2 reductions breakdown

We worked with a team of graduate students at Yale’s Center for Business and the Environment to evaluate the environmental impact of our digitally native supply chain and to compare this against traditional industrial shoemaking. To the best of our knowledge, this is the first environmental assessment of 3D printed shoes. The headline numbers illustrate the impact our way of making things can have. HILOS shoes reduced carbon emissions by 48% and water usage by a full 99% compared to industry competitors. Yet there is more to the story than simple, unbridled improvement. Learning what’s behind these numbers has given us new insight into how sustainable supply chains can be reshaped to be even more effective.

Is circularity enough?

Before the study, we predicted that product recycling across our reverse supply chain would have a major impact on overall emissions. Instead, it only reduced our carbon footprint by 7.25% – and that was assuming a 100% product return rate. The real impact of product circularity would likely be much less. If only a quarter of customers actually return their shoes, it would drop our carbon footprint by less than 2%. This is largely because of the energy required to reprocess material for a second life. If those recycling processes had been carbon neutral, product circularity could reduce carbon emissions (in our case) by up to 22%. That’s a material difference, and one worth investing in. The conclusion? Increasing the efficiency of material renewal is key to leveraging the full potential of product circularity.

What mattered most?

Product design had far and away the greatest impact on material waste. A typical shoe can be made up of 65 discrete parts assembled in 360 steps. By contrast, HILOS’ Emmett is made from five parts assembled in twelve steps.

  • Assembly image

Every part of a shoe produces waste in getting made. With new forms of shoemaking designed for 3D printing, we were able to consolidate parts normally made separately. For example, instead of having an insole, midsole, outsole, and shank, we print a single piece, slashing material waste as well as the emissions from assembly. Altogether, part and material reduction accounted for a 29% drop in carbon emissions. That combined with only making products that would actually be sold had the most dramatic impact on carbon reduction, jointly reducing carbon by 43%. This is a conservative estimate. It is extremely complex and difficult to identify the yield of every process that goes into making a shoe, especially one that can have 65 components and 360 assembly steps, so for now, we are only taking into account the material that went into the product itself. Our key takeaway: the right design and application of 3D printing is critical for overall carbon reduction.

Putting it all together

This means circularity is only one part of the equation. Even if everything we made today was 100% returned and recycled, manufacturing is still a wasteful and resource-intensive process. Brands overproduce. In apparel, this sometimes means making as much as 35% more than is needed. We can avoid creating and recycling shoes no one needs by only crafting on-demand, after a customer makes a purchase.

Making fewer shoes, while selling the same number, has an enormous impact across the entire supply chain – even more than you might initially imagine.

As an example, a single cow hide can produce ten pairs of uppers and be one fifth scrap. Injection molding can make a hundred outsoles at 50% yield, meaning half the material is wasted between molds in the mold channels. Even if you manage to collect and reuse most of this waste, reuse has its own footprint. Every time you make something, there’s waste above and beyond the amount of material in that product.

When you reduce overproduction, you’re not just preventing the materials that went into that product from being wasted -- you’re preventing the waste that accompanied every part of the process.

Moving forward, we will focus far more attention on part reduction and on-demand manufacturing to drive a more sustainable and efficient supply chain. Product circularity remains a focus across everything we do, but we now understand that it will not have the impact many of us hoped for on its own.

A sustainability lead for an apparel brand once told us that the most sustainable clothes in the world were the ones already in our closets. They were right: prevent something unnecessary from ever being made, and you can really change the world. If HILOS has one purpose, that’s it.

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