The Road to 100% Bio-Based PU for Footwear

Recently INSITE Director of Innovation Dr. Caleb Dyer spoke at the AMI Polymers in Footwear conference in Portland, OR, delivering a presentation titled The Road to 100% Bio-Based PUs for Footwear.

In his talk, Caleb focused on the obstacles and opportunities facing the footwear industry as it shifts to using more planet-friendly materials. He also addressed the ways INSITE and its material partner Susterra® are working to overcome these obstacles — and where we’re headed next.

Read on for a summary of Caleb’s presentation, and join us as we continue the discussion at the FDRA Shoe Sustainability Summit in Portland on Sept. 17th.

Feedstocks Matter

One of the most popular materials used in footwear since the 1960s is polyurethane (PU) foam.

Polyurethane is the result of a reaction between polyols and isocyanates, typically from a petrochemical source. When it comes to bio-based PU, bio-based polyols are nothing new. These plant-based compounds are often derived from vegetable oils like castor, corn, or beets. But many of these feedstocks present several challenges:

First, the agricultural impact of these feedstocks can diminish the environmental savings they offer due to unsustainable farming practices.

Next, the physical properties of the materials these compounds produce can be volatile, leading to issues with scalability.

Last, many of these feedstocks are used as fillers, rather than a reactive part of the process, which makes engineering foam to meet specific properties difficult.

In response to these challenges, many brands turn to recycled plastics to minimize their burden on the planet. But recycled materials pose their own hurdles to footwear developers, including lack of sourcing transparency and degradation of quality with each cycle.

What Makes a Great Feedstock?

There are several components of a great bio-based feedstock. In terms of sustainability, a feedstock needs to be:

1. Transparent: Sourcing data must be readily available and presented with integrity.
2. Relevant: Environmental savings directly impact the health and well-being of consumers, especially the reduction of carbon emissions.
3. Measurable: Claims are tied to repeatable testing and industry-standard metrics.

While increasing sustainability is the leading goal of bio-based materials, feedstocks must also produce a viable product solution. This requires the compounds to be:

1. Durable: The end material must hold up to the same wear testing rigors as any other footwear component.
2. Comparable: The compound must meet or exceed consumer expectations for cushioning and comfort.
3. Engineerable: Physical properties must be flexible to meet the specific needs of footwear developers.

How Susterra Measures Up

INSITE® EcoComfort® foams are made with up to 70% plant-based content thanks to Susterra® propanediol, derived from U.S. grown dent corn. 

As an example, INSITE EcoComfort Terrain F71 comprises 50% Susterra propanediol in its total compound blend. In terms of sustainability, here’s how Susterra measures up:

• Transparency – Susterra gives us some of the more robust third-party LCAs of bio-based suppliers
• Relevance – Most of Susterra’s LCA is concerned with the reduction of carbon, which is one of the most relevant metrics for measuring the impact of INSITE EcoComfort foams
• Measurable – Thanks to the Truterra program, Susterra tracks 100 data points at the field level, including things like soil quality, nitrogen use efficiency, and GHG emissions

When compared to INSITE Terrain F20, a petrochemical-based alternative with similar hardness and density, EcoComfort Terrain F71 offered:

• Durability – We see similar tear and tensile strength, with a significant increase in elongation properties
• Comparability – Not only do we get comparable physical properties, but we also see some improvements to resilience and compression set
• Engineerability – Because Susterra plays an integral part in the reaction process, we can tailor physical properties with greater specificity

Addressing Challenges

The largest challenge facing any corn-based solution is agricultural impact.

Traditionally, corn farming is heavily subsidized and resource intensive. To address these issues, Susterra is partnered with the Truterra® program to support farmers in their efforts to  implement regenerative farming practices.

Because dent corn has a strong supply chain, it allows us to scale to the level of commercialization required to meet the needs of large footwear brands. And when used as a bio-based polyol, it becomes an integral part of the reaction. This creates better and more adaptable material properties.

READ MORE: The Truth About Corn: Ethical and Sustainable Sourcing

The NEXT Challenge: Bio-Isocyanate

With several plant-based polyol options available on the market, we’ve already solved 70% of the equation for producing a truly bio-based polyurethane. The next step is developing the bio-based isocyanate.

While it sounds straightforward, this is where the industry has effectively hit a wall, struggling to create a viable solution that is both sustainable and scalable. Where petrol-based isocyanates have a steady stream of feedstocks with high efficiency, sustainable alternatives still face challenges.

First, many bio-based feedstock crops yield too little to meet the demands of large-scale production.

Similarly, bio-isocyanates have a lower reactivity than their petrol-based counterparts, which leads to a lower yield of the polyurethane compound.

While bio-based isocyanates eliminate the need for fossil fuels, the conversion process still requires both the input and output of harmful chemicals, negating any environmental benefit that comes with the absence of petroleum.

As with bio-based polyols, an effective bio-based isocyanate has to meet strenuous standards in order to meet both the sustainability and scalability requirements for footwear success.

A Long Road Ahead

The road to 100% bio-based PU may seem long, but achieving this milestone is not out of reach. The footwear industry is no stranger to innovation and new ideas continue evolving daily.

At INSITE, we’re committed to working towards a more sustainable future for footwear. To learn more about our dedication to sustainability, visit https://insiteinsoles.com/sustainability/.