Dielectric failure and optical switching failure in electro-fluidic display (EFD) is still a bottleneck for sufficient device lifetime. In this study, a dielectric redundancy-designed multilayer insulator of ParyleneC/AF1600X was applied in an EFD device. The reliability performance was systematically studied by tracking the applied voltage dependent leakage current and capacitance changes (I-V & C-V curve) with thermal aging time. The multilayer insulator shows a more stable performance in leakage current compared to that of single-layer insulator. The failure modes during operation underlying the single layer and the multilayer dielectric appear to be different as exemplified by microscopy images. The single layer AFX shows significant detachment. In addition, by quantitatively analyzing the C-V curves with aging time, we find that for the single AFX device, the dominant failure mode is “no-opening” of the pixels. For the muti-layer device, the dominant failure mode is “no-closing” of the pixels. This study provides tools for distinguishing the basic failure modes of an EFD device, and demonstrates a quantitative method for evaluating the reliability performance of the device under thermal aging.