Why does PU soles sometimes crack on its own?

Why are there small holes in my foot soles? What should I do? - Quora

The 8 Best Boot Soles You Should Know About

The 8 Best Boot Soles You Should Know About

UPGRAGE DESIGN - The upgraded heel protector with air holes is more breathable and moisture-wicking, keeping your feet nice and comfort. Made of

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Why does the sole of my leather shoes come off when I use it after storing it for a long time? Why does this happen and what should I do to prevent

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Why have my soles collapsed?

What could be some reasons that the soles of my feet keep getting crackly dry? - Quora