The problem is due to a process known as hydrolysis. Hydrolysis is the chemical breakdown of the PU polymer and the resulting disintegration of the PU sole accelerated by the high humidity in tropical climates. As a consequence, PU loses flexibility over time and gradually becomes brittle, and starts cracking and crumbling. The aging of safety shoes is an entirely normal process that all PU-soled shoes go through. With proper care and storage of safety shoes in a dry and well-ventilated space, hydrolysis should not be a common problem.