A resistive element of the capacitor model found in both the AC and DC domains. Contributing factors: electrodes, leads, dielectric. This value can change with frequency, time, etc. A measure of the total lossiness of a capacitor which includes the leads, electrodes, dielectric losses, leakage (IR) and most important, the end spray connecting the leads to the metallized film. The lower the ESR the higher the current carrying ability the capacitor will have.