Medium particle silica functions as a spacer by balancing the particle size distribution of external additives, contributing to thermal stability during high temperature storage while ensuring both toner flowability and charge stability. It provides stable charging and consistent print quality without excessive scattering. The particles adhere appropriately to the toner surface without being easily buried or detached, contributing to longer toner life and consistent performance. It is advantageous for charge control and enables uniform toner supply even in high speed printing. These characteristics are particularly beneficial for maintaining the long term performance of color toners and fine particle toners. Various surface treatments and particle size adjustments are available to optimize formulations.