Coated fabrics featuring plasticised poly(vinyl chloride) (p-PVC) and thermoplastic polyurethane (TPU) coatings are widespread in fashion collections. These materials pose significant conservation challenges due to their production and chemical variability, coupled with issues of rapid deterioration. Despite their prevalence and instability, systematic research on their composition and ageing behaviour remains limited, as most studies rely mainly on infrared spectroscopy and cover a small number of cases, which cannot fully capture their chemical complexity. This knowledge gap represents a pressing issue, as it hampers the development of well-informed conservation strategies. This research addresses this gap by investigating a representative set of twenty-five historical and contemporary fabrics from the 1990s onwards, coated with aromatic and aliphatic polyester-based TPUs, as well as phthalate- and terephthalate-plasticised PVCs. Samples were characterised using a multi-analytical approach combining optical microscopy, infrared spectroscopy, pyrolysis–gas chromatography/mass spectrometry, and X-ray fluorescence spectroscopy. This integrated strategy provided unprecedented detail on the chemical variability of p-PVC and TPU-coated fabrics, enabling the identification of primary components, additives, degradation products, and mixed compositions. This study underscores the value of multi-technique analysis to capture the complexity of such coated fabrics, providing essential knowledge for further research and development of effective conservation strategies for fashion collections.