What’s Really Inside Your Running Shoe? Unpacking Footwear Material Innovation

Credit: cora-pursley

10 February 2026

You might think the biggest challenge in running shoes is performance: speed, cushioning, energy return. The harder problem lies in material compatibility: how do you create a cushioned midsole that’s light, responsive, and durable, while also being recyclable? How do you bond different materials together strongly enough to withstand thousands of impacts, but reversibly enough to separate them later? These aren’t just design questions, but materials science problems. In this article, we unpack the hidden complexity of running shoes, the challenges of conventional materials, and where the highest potential for material innovation lies.

Source: Fashion for Good

THE ANATOMY OF A RUNNING SHOE

Strip away the idea of a shoe as a single object, and you’ll see something more like a building: a structure made of interconnected layers and systems, each serving a critical function. In fact, a running shoe is a small miracle of engineering, and a puzzle for sustainability: it’s a carefully orchestrated assembly of 60+ distinct components, each with its own purpose, material composition, and role in how the shoe performs. 

The Insole and Insock are the parts closest to your foot, but they’re two distinct components working together. The insock (sometimes called a sockliner) is the thin textile layer your foot actually touches, typically made from fabrics like polyester, cotton, viscose, wool and blends, with light foam padding made of PU  (Polyurethane) or EVA (ethylene-vinyl acetate) beneath for comfort and moisture absorption. Sitting below that is the insole itself, a structural layer made from materials like EVA, PU or TPU  (Thermoplastic Polyurethane) that helps shape how force is distributed across the foot. In some shoes, these layers are glued in permanently. In others (the more circular designs), they’re modular, meaning you can remove them, replace them, or upgrade them without discarding the entire shoe.

The Upper is a multi-layer wrap designed to support your foot and manage moisture. It typically includes a mesh exterior for breathability, reinforcement panels for stability, and foam padding for comfort. This is where you’ll find polyester, nylon, canvas, or increasingly, recycled textiles, and several types of blends.

The Sole, the foundation: actually a sandwich of three layers. 

• The outsole makes contact with the ground and is typically made of rubber (synthetic or natural), EVA and TPU designed for grip and durability. 
• Above that sits the midsole, the cushioning layer where EVA foam, polyurethane, or newer thermoplastic elastomers do their work, absorbing impact and shaping how the shoe performs. 
• Then there’s the stobel board, a thin layer that sits between the midsole and upper (though its presence depends on the construction type). This is usually made from non-woven polyester, felted cellulose (viscose/lyocell) and blends. 

Keeping the whole shoe together is the Assembly. Everything is joined together using adhesives or stitching, or a combination of both, or by direct fusing of the upper and sole. And scattered throughout are fasteners, laces, eyelets, labels, and fabric patches; small components that are easy to overlook but surprisingly complex to separate for recyclers.

Few realise that the sole holds the key to reducing footwear’s environmental impact. The whole sole is often the first part to wear out, and when it fails, the entire shoe’s performance drops, turning otherwise usable shoes into waste. Besides this, there’s another truth behind why we should focus on the sole, and especially, one of its elements: the midsole alone accounts for up to 75% of a running shoe’s weight, so changing its material has the highest per-unit impact potential on carbon footprint. This dual problem (that soles fail first, and that the midsole dominates the shoe’s weight and impact) makes the sole the highest-leverage point for innovation.

THE MATERIAL CHALLENGE

Most conventional footwear today is still built from fossil-fuel-based plastics and synthetic rubbers. EVA foams, TPU, PU, synthetic rubber outsoles, and polyester uppers are all materials that start their life as fossil resources. Along the way, many of these materials are processed using chemical additives, solvents, and adhesives that can include phthalates, heavy metals, and other substances of concern. These play a role in making shoes perform well: lighter, softer, more durable, and more flexible. But they also make shoes harder to recycle, harder to disassemble, and riskier from a health and environmental perspective. Once multiple materials and chemical formulations are permanently glued together, they’re no longer just a product, but a composite waste problem.

So why not simply switch to “better” materials?

Because in footwear, every material choice is a balancing act between performance, cost, scale, and supply chains. Changing a midsole foam can affect cushioning, energy return, durability, weight, manufacturability, and ultimately whether runners trust the shoe with their bodies. On top of that, new materials often come with higher premiums, limited volumes, and longer performance testing times. This is the tension at the heart of footwear innovation: how do you radically reduce impact without compromising the function people rely on?

What does “better” actually mean?
A truly future-fit running shoe material should:

• Extend the life of the product through durability, repairability, or replaceable components.
• Be recyclable without losing value or performance, not downcycled into something of lower value, but kept in a high-quality loop.
• Use safer inputs, non-toxic chemicals, no PFAS, fewer harmful solvents and glues, and ideally bio-based additives.
• Reduce dependence on fossil feedstocks by using bio-based or recycled inputs for polymers.
• Be designed for its end-of-use from the start, meaning the material chemistry itself is engineered to be taken apart, reprocessed, or remade.

WHAT ARE THE MATERIAL INNOVATIONS IN FOOTWEAR?

A growing number of innovators are working on materials that address some of these challenges. While many are still in development or early commercialisation, they represent important directions for the industry. Here’s what’s emerging:

Bio-based materials use renewable feedstocks like plant-based oils (castor oil, hemp oil), plant starches (from sugarcane, corn), algae oil, and even carbon capture as alternatives to fossil fuels. Here are some examples:

• Bio-based EVA can be produced by deriving ethanol from bio-based feedstocks such as sugarcane, producing ethanol from carbon capture, or using macro-algae as a feedstock. Some of the innovators in this space that caught our eye are LanzaTech and Bloom Materials. 
• Bio-based PU and TPU are being developed by companies like Algenesis Labs and Evoco (both innovators participating in our project The Next Stride, aiming to validate the performance and environmental impact of bio-based polymers as sustainable alternatives to the fossil fuel-derived materials currently used in footwear soles). These materials derive algae oil from microalgae or other non-food sources to make starting materials for PU foams.
• Bio-based TPE (Thermoplastic Elastomer) is being developed by innovators like Balena and Kuori (also both participating in the Next Stride project). They’re replacing traditional fossil-fuel-based TPE components with bio-derived alternatives and incorporating natural fillers like natural fibres, natural carbonates, certain types of clay, and food side streams like pits, peels and shells. 

Rubber, which is usually used in outsoles for grip and durability, seems naturally sustainable, but conventional production often drives deforestation. The solutions:

• Responsibly sourced natural rubber that carries Forest Stewardship Council (FSC) certification, ensuring it comes from well-managed forests that protect biodiversity. An example of innovation in this space is NFW with its PLIANT, a material designed to combine performance with responsible sourcing, offering a sustainable alternative for footwear outsoles. 
• Alternative rubber sources like guayule or dandelion rubber can grow in arid or marginal lands that can’t support food crops. Some innovators, like Reselo, are even upcycling waste from other industries (like birch bark) into rubber-like materials.
• Rubber alternatives include materials grown from mycelium, algae, or other biological sources, plus plant-based curing agents that replace traditional sulfur-based vulcanisation.
  

The path forward for running shoe materials isn’t about finding one perfect solution, but building a portfolio of innovations that work together. As bio-based polymers, responsibly sourced rubbers, and circular design principles move from lab to production scale, the industry faces a practical test: can these materials deliver the performance runners demand while genuinely reducing environmental impact? The answer will depend not just on material science breakthroughs, but on whether brands, manufacturers, and consumers are willing to rethink what makes a shoe worth buying, and worth keeping.