Today’s “Sneaker Ingredients” feature focuses on vulcanized rubber, the foundation upon which modern footwear was born. Continue reading for a detailed look at this formative ingredient…

Before there was EVA and Phylon, there was vulcanized rubber. Vulcanization is a process whereby rubber molecules, or polymers, are linked by combining liquid rubber with sulfur and then heated. The heat allows the chemical structure of the rubber to transform into a more usable substance than stock natural rubber or synthetic rubber – and it is approximately 10 times stronger than either original version. The result is a very elastic, durable rubber that can be used in many applications including heavy-duty products such as tires, shoe soles, hoses, and boots, as well as less utilitarian products such as weather stripping, hockey pucks, and watch bands. The vulcanization process is versatile because it can be applied to both natural rubber and synthetic rubber.

Christopher Columbus introduced rubber to the western world but it was originally developed by Indians of South and Central America. They called it caoutchouc, a derivative of the word cahuchu meaning “weeping wood”. The story goes that inventor Charles Goodyear stumbled upon the vulcanization of rubber in 1839 when he accidentally dropped some gum-and-sulfur mix onto a hot stove. He found that rather than melting into a syrupy consistency the mix hardened into a leather-like texture. So enamored of this new miracle material was Goodyear that he wanted to make virtually everything out of rubber – money, flags, musical instruments, ship sails, and even ships themselves. He also wore rubber hats, vests, and ties. Goodyear is officially credited as the creator of vulcanized rubber, and the multi-billion dollar Goodyear Tire & Rubber Co. was named after him to honor his discovery and years of work.

To make vulcanized rubber, a base rubber must first be produced. For natural rubber, the sap of the Pará tree is collected. Synthetic rubber is made from a cocktail of monomers, or small molecules, that may be cross-bonded. An example of a natural monomer is glucose, a simple sugar. Final products can be shaped during the vulcanization process or stamped from the cooled rubber afterwards. It is in these implementations that the material is ideal for footwear manufacture.

Today, vulcanized rubber is used in countless footwear. Shoe models that best showcase the textile include the Converse Chuck Taylor All-Star (midsole/outsole), PF Flyers Center Hi (midsole/outsole), and Vans Classic Slip-On (midsole/outsole).

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Sample our previous “Sneaker Ingredients” batches:

- Sneaker Ingredients: Thermoplastic Polyurethane (TPU)

- Sneaker Ingredients: Neoprene

- Sneaker Ingredients: Suede