The series resistance, Rs, represents the resistive losses in the windings. The parallel capacitance, Cp, is the equivalent capacitive effect between the turns of the coil, and the parallel resistance, Rp, is the sum of all losses in the core. Open flux inductors are more sensitive to metallic materials that are in close proximity, because such materials modify the magnetic field. Toroidal inductors keep the flux inside the core and are less sensitive to external conductors in close proximity.