Electrical cable for submersible pumping systems must be of high quality and reliability. Because of this, careful selection must be made of materials which will optimize performance in a wet electrically stressed environment. Polypropylene is the insulation used in lower temperature cables which is a major part of this cable market. Over the past eight years a major engineering effort has been placed on the evaluation of polypropylene resins and their wet electrical properties. Test methods were selected which distinguish between resins based on long term electrical stability. Properties of most extrusion grade resins available together with some experimental resins will be reviewed. Dielectric breakdown, insulation resistance, dielectric constant and power factor all versus time will be presented. The data will demonstrate the need for long term evaluations prior to the selection of a polypropylene insulation for ESP cable applications.