When designing ferrites, a number of capabilities are considered when developing a part. A good flux density saturation point is important to take into account, especially for power applications. Also important for that same application are low power losses for maximum efficiency. Taking into account the operating environment, extreme heat will cause permeability to drop, so a good Curie temperature is needed for those situations. What are the mechanical constraints limited for each application? Weight, outer diameter or inner diameter of the core, length of the core or rod, or shape and depth of various E-cores are just a few things to take into consideration.