Why Your Shoe Soles Crumble Over Time: The Science of PU Hydrolysis

If you have ever pulled an old pair of shoes from the back of your closet only to find the soles cracking or turning to powder with each step, you have witnessed a common material failure known as PU hydrolysis. This breakdown is not simply a sign of wear but a chemical process intrinsic to standard polyurethane (PU) when it ages under specific conditions.

Polyurethane is favored in footwear for its excellent cushioning, flexibility, and durability. However, its Achilles' heel is its susceptibility to moisture. The ester bonds in the PU polymer chain are vulnerable to reaction with water, especially in humid environments. Over time, this reaction severs the molecular chains, causing the material to lose its structural integrity. The sole becomes brittle, crumbles, and ultimately fails. While the typical timeframe for noticeable hydrolysis is often cited as three to five years, this period can be significantly shortened by factors like consistent exposure to humidity, heat, and inadequate storage conditions.

For footwear brands, this presents a clear challenge to product longevity and customer satisfaction. The solution lies in proactive material engineering and selection. Factories can combat this issue by adopting hydrolysis-resistant PU formulations. These advanced materials incorporate stabilizing additives, such as carbodiimides, which act as scavengers for the moisture and acidic byproducts that accelerate breakdown. Alternatively, switching to polymer blends with inherently higher moisture resistance, like certain grades of thermoplastic polyurethane (TPU), can dramatically extend the functional life of the sole. Beyond material choice, thoughtful design also plays a role—improving sole ventilation and reducing moisture traps can mitigate the environment that leads to hydrolysis.

At HUADONG HOLDINGS GROUP CO., LTD, we have dedicated over three decades to mastering polyurethane technology for footwear. Our expertise extends far beyond basic manufacturing. We develop and supply advanced PU sole compounds engineered specifically for superior hydrolysis resistance. We understand that trust requires proof, which is why our materials can be supported by official anti-hydrolysis certification from independent, professional testing institutions. This certification provides tangible, data-backed assurance for your brand and your customers.

Let us partner with you to build footwear that lasts. From material science to mold design, we provide end-to-end solutions. Choose HUADONG to craft the foundation of your next collection—where durability is engineered from the ground up.

Contact HUADONG today to begin customizing your high-performance soles and molds.