The
molecules of a material are either electrically unsymmetrical, dipoles, or totally symmetrical and are then uninfluenced by electric fields.
There
can also be movable electric charges, free electrons or ions, in a material. Then it has
conductivity.
In
a matter with dipoles these try to follow the direction of the electric field by turning around. Heat is then produced by friction. Likewise is heat produced by friction when ions are moved by a field.