An innovative electrostatic charge decay (ECD) technique previously introduced has been shown to be a good predictor of charge roller performance. The physical reason behind the correlation between ECD and charging performance is that both processes depend on dielectric relaxation to rearrange the charge distribution in the resistive layer. In this paper, we present experimental and theoretical studies of dielectric relaxation in resistive materials used for charge rollers. It is shown that the process can be non-ohmic, and that information on charge injection and transport parameters in addition to resistivity is required for specifying an effective charge roller.