Stator coils in modern air cooled generators are subject to high electrical, mechanical, and thermal stress. In addition, operation in the air environment doesn't offer the dielectric advantages of operating in high pressure hydrogen. These three insulation stress factors are well known and for the most part understood with respect to the factors taken into account when designing air cooled generator stator windings. These three stress factors are considered when selecting the coil materials, the coil geometry, and the rating capabilities of the stator coil. With the movement to increasing the power density of air-cooled generators, it has become more critical to be sure the design constraints are met in the stator coil design. In addition, the coil materials and processing must be improved to meet the demands of the increased stress factors. In addition to the use of high performance coil materials, great improvements have been made in the analysis, testing, and the use of more sosphicated instrumentation for verification testing. The stator coil insulation system used in the modern air cooled generators are designed to meet the high demands placed on the system during generator operation.