App note from Vishay about how modern power inductors are made and their performance. Link here (PDF)
Power inductors are typically used for energy storage in DC/DC converters or high current noise filter applications, including motor speed control, adjustable lighting, DC power conditioning, and more. Power inductors can be divided further into two groups – shielded and unshielded. Unshielded power inductors have an open magnetic circuit where the magnetic flux induced in the core by the current in the winding exits the core and extends through the air to the other side of the core where it completes the flux path.