There are two ways to wind the core for a common mode choke. The first is using sectional windings. This is made up of two independent windings wound separate of each other. The second would be the Bifilar way of winding which incorporates two wires wound around the core together. As will be shown in the next couple of slides, bifilar windings do not improve differential mode impedance whereas Sectional windings will. Würth supplies common modes with both types of windings.