The selection of core material dramatically influences the operation, efficiency and cost of magnetic devices such as motors, transformers, and relays etc. The core material, therefore, is of prime interest to designers. Although there are many materials that have been established, by long-time design and production experience, to be suitable for general applications, it is the specific requirements of each application that determines the magnetic characteristics that must be considered in selection of the best suited core material.

There are various factors and requirements that must be considered for proper selection of core material. In most cases a combination of requirements such as efficiency, heat rise, output torque, etc. are necessary to meet the design needs. In such cases there are materials that can provide an effective combination of good magnetic properties to meet the application. In other cases like magnetic devices such as some relays and garage door openers, where the device operates only a few minutes a day, minimum cost is the main requirement Still in other applications, such as generators, high residual magnetism is the principle requirement

Mechanical and physical characteristics of core materials must also be taken into consideration to meet design requirements and to minimize manufacturing and fabrication difficulties.

Traditionally, cost has been the prime consideration in magnetic device selection and it will continue to have a high priority. However, as a result of increased energy cost and the need for energy conservation, efficiency is becoming a more important consideration in selecting and purchasing magnetic devices and materials.