Electromagnetic induction coils are widely used in a variety of applications, such as motors, solenoid valves, and relays. Many of these applications are safety-critical. Failure of the insulation that protects the windings in electromagnetic coils is a significant cause of coil failure and can have severe implications for system reliability. An effective insulation health monitoring program can reduce maintenance and replacement costs, predict the useful lifetime of the coil, and improve the operational availability of the system in which the coil is used. Impedance monitoring of coils has emerged as a promising approach for non-invasive, in-situ insulation health assessments of electromagnetic coils. Yet, little was understood about the relationship between coil impedance and traditional insulation health metrics, such as insulation capacitance and insulation resistance. Furthermore, relating the impedance measurements to chemical and mechanical characteristics of the insulation material is important to understanding the relationship between impedance measurements and the state of the insulation at failure. This study describes the development an improved method of electromagnetic coil insulation health monitoring and shows the uncovered relationships between coil impedance and the insulation electrical, chemical, and mechanical properties.