Polymers are the essential part of modern life, found in everything from household products to advanced engineering materials. In situations when there is no proper documentation, understanding their structure, composition, and manufacturing history becomes extremely important. Reverse engineering, through careful mechanical breakdown, is a comprehensive method used to uncover the mechanical, molecular, morphological, and thermal properties of finished polymer products. This chapter explores the concept and significance of reverse engineering in understanding polymer materials and developing correlations between their structure and properties. To study polymer composition, morphology, additives, and performance, it uses widely applied analytical techniques such as FTIR, DSC, TGA, GPC, SEM, NMR, and XRD. Real-world examples, including the reconstruction of vehicle parts, multilayer food packaging, and the modification of safety glass, highlight the practical value of reverse engineering in ensuring regulatory compliance, improving reliability, and enhancing design quality. Overall, this method is a valuable tool for material replacement, advancement, and performance improvement across various industries.