These shapes are available in lamination materials (for stacking), powdered material (typically powdered iron), and ferrite materials. In laminated form, their features are similar to that of the C core discussed in a prior section. Heat dissipation is excellent. There is lots of room available for lead wires. Self-shielding is poor. U cores have two core legs. Coils can be placed over either or both legs. Using coils on separate legs is great for high voltage isolation between coils. The mean turn length of two coils on separate legs (sharing the whole winding window) is smaller than 1 coil on one leg (occupying the whole winding window), hence the two coils connected in series has less winding resistance. U (and C) cores may be used for split-core current transformers.

Core Types Used by Butler Winding