Rare insults

Hydrolysis. Allegedly using shoes with PU soles often squeezes moisture out of them, preserving life, but idk if that's actually true. I can definitely say heat combined with humidity will definitely degrade it pretty quick. Density of the PU really matters, though, cause some PU soles that are relatively rigid (like regular Chaco sandals) are basically bulletproof, while the more cushiony forms with air injected (like the Chaco "cloud" sandals i mistakenly bought, or blundstones) will break apart.