The Best Use of Renewable Feedstocks for Insole Foam

by | Mar 22, 2023 | Sustainability

From Corn to Castor Oil, Feedstock Sources Make a Difference

The use of renewable feedstocks, such as corn, sugar beets, and algae, are growing in popularity to make sustainable materials for different products. But what do these feedstocks really deliver in terms of quality and sourcing responsibility? This post explores the important differences among feedstock sources and what brands should look for when seeking more sustainable insole foams.

Digging into What “Sustainable Materials” Actually Means

Sustainable insole foam – sounds great! But what does “sustainable” really mean? We know that brands are discerning when it comes to adopting new materials, and the broad use of “sustainable” can leave a lot of questions on the table about sourcing and quality.

A recent article from Well+Good addresses this very question: what does it take to make a sneaker truly sustainable?

The biggest point the article makes is that sustainable footwear is only truly sustainable if the practices used to make the sneaker are as well. Fossil fuel-derived materials and pollution-causing manufacturing processes are cited as big contradictions to any claims of planet-friendly footwear.

It’s tough for brands to keep up with consumer demand while simultaneously overhauling sourcing and manufacturing. The best solution to being truly sustainable is to identify sustainably-sourced materials that produce sustainable products, but understandably, it can be tough to know where to begin, or if sustainable material choices are the correct ones.

For the purposes of this article, we’re going to focus on the sourcing of different feedstocks used for sustainable insole foams. The insole is a critical part of any shoe, and should always be included in the sustainability equation.

What are Renewable Feedstocks?

Let’s start with a definition for both depletable and renewable feedstocks.

Depletable feedstocks include finite natural resources like petroleum, coal, and natural gas, which are being used for many human activities but cannot be replenished – at least not for many thousands, or even millions, of years.

A renewable feedstock, on the other hand, is any material that can be converted into another form and used again. One of the more broadly-known examples of a renewable feedstock is biomass, which is derived from plants. When plants are used as feedstock for products, such as insoles, new plants can be grown on a human timescale to replenish the supply.

We have identified a short list of different renewable feedstocks that can be used to make insoles. Some of these options include:


Industrial field corn


Castor oil



Let’s take a deeper dive into these renewable feedstock options and some of the important ways the sustainability of the resulting material can be increased.

Renewable Feedstocks for Insoles: A Closer Look

While we are focusing on insoles for the purposes of this article (and for obvious reasons), these renewable feedstocks have uses for many different types of products, including footwear uppers.

Industrial Field Corn

Plant-based bio-propanedial (or bio-PDO) is frequently made from industrial field corn and replaces some of the main petrochemical ingredients in polyurethane (PU), which is a primary insole foam material. Bio-PDO is not a filler or additive – it’s an integral part of the chemical reaction, making it a better-performing foam compared to other plant-based alternatives.

At INSITE, the industrial field corn used for our bio-PDO is also made using regenerative farming practices, adding to the sustainability of the material.

How does it perform? Bio-PDO creates a stronger blend of plant-based material, ultimately making the foam more comfortable and enhancing its performance. Other benefits include greater tear strength, tensile strength, and elongation, which are all important features for increased insole comfort, performance, and support.

Castor oil

Castor plants are abundant but until recently have had very little modern-day uses. Not only does the castor plant replenish quickly – a single castor plant can grow up to 15 feet in a single season – but it can also yield a high percentage of castor oil, the renewable feedstock that brands are beginning to incorporate into different products, including footwear and insoles.

Oil is extracted from castor seeds through a drying and hardening process, and is then removed of toxins. To become a foam insole material, the castor oil goes through a chemical reaction called transesterification, which converts the oil into polyol, a complex alcohol. By creating polyol using castor oil rather than the more standard process of using fossil fuels, the foam production becomes far more sustainable.

How does it perform? Using castor oil for insole foam results in comfortable insoles with a high level of rebound. What’s more, they’re highly durable thanks to the castor’s high viscosity and stability.


Many brands have taken advantage of algae as a renewable feedstock for insoles and other products. Algae is a unique renewable feedstock; one noticeable byproduct of water pollution and climate change is the rampant growth of algae blooms, which can be harmful to ocean health in such great numbers. By removing excess algae and using it as a renewable resource, the sustainability benefit is multi-fold.

Algae can be harvested for CO2, which is then sequestered and used in the manufacturing process. For producing materials like insoles, algae can be dried, turned into a pellet, and injected into bioplastic sheets, increasing the sustainability of that material.

How does it perform? Algae produces high-comfort material and as far as insoles go, it would be tough to tell the difference.

Aside from sustainability, why consider a plant-based insole for your footwear products?

In general, plant-based materials offer greater strength features, allowing insoles to be made lighter but with higher durability, ensuring they last for the lifetime of the shoe.

How is INSITE Pursuing Truly Sustainable Insole Material

We are proud partners with Susterra, which helps brands implement sustainability practices and materials into their products.

Using bio-based materials, like industrial field corn, INSITE is able to maintain or enhance important insole features such as breathability, durability, comfort, and support while reducing the environmental impact right at the source. And based on our ProvenComfort testing, Susterra offers some of the best biomechanical benefits for our patented ergonomic shapes as well.

If a brand is using a sustainable material, but sourcing it using non-sustainable practices, the sustainability claims become less impactful. We’re on a mission to be sustainable from source to product so brands can be confident in the environmentally-friendlyness of their products.

To learn more about INSITE’s sustainability practices, request a copy of our white papers today.

Insole Insights