In this work, we explore the complexities introduced by polymorphism in malware families, a tactic used by malware authors to alter the appearance of their code and evade detection mechanisms, resulting in a growing volume of unique malware samples. We examine 66,160 malicious Portable Executable (PE) files grouped into 743 families from three popular malware datasets. Our research addresses three key questions: measuring structural component-level differences between PE files, identifying prevalent polymorphic techniques affecting multiple components, and pinpointing component-level causes of polymorphism. We introduce a methodology for component-level structural comparison of PE files and apply it to investigate the diversity and similarity of samples within a family, considering factors such as packing and truncation. Our study reveals that polymorphism in malware is driven by multiple overlapping factors, extending beyond just the use of packing tools. These findings highlight the complex nature of malware families and inform future research, improving our understanding of malware variations and their implications.