PU Midsole Disasters! Is Polyurethane Foam a Poor Choice?

PU Midsole Disasters! Is Polyurethane Foam a Poor Choice?

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Understanding Hydrolysis and Polyurethane in Shoe Manufacturing
In the shoe manufacturing process, the soles are often attached to the uppers by combining two materials in a mold, which leads to a chemical reaction resulting in the formation of polyurethane (PU). Polyurethane is favored for its lightweight and flexible properties, making it an excellent choice for shoe soles. Not only does it offer excellent shock absorption, but it also boasts remarkable durability, making it ideal for footwear.

However, one significant challenge associated with polyurethane is the natural aging process known as 'hydrolysis.' Hydrolysis refers to the chemical breakdown of the PU polymer, leading to the physical disintegration or crumbling of the PU sole when exposed to water (usually in vapor form). Surprisingly, this deterioration can occur even when the shoes are in storage, taking place over the span of several years.

The speed of this hydrolysis process is accelerated by warm and highly humid environments. As a result, it occurs more rapidly in tropical climates. Additionally, storing shoes in confined spaces like lockers while damp can also expedite this degradation. In the most advanced stage of hydrolysis, the PU sole loses all its physical strength, eventually leading to cracking or crumbling.