used as oil gap insulating for transformer. Its advantage is in assembly. It improves the distribution of oil channels in solid insulation material comparing with the strips radially arranged evenly in the oil channel of corrugated board. The solid insulation is very even. There is no surface which is perpendicular to electric field, therefore it can increase the strength of the oil channels by 15% without losing its reliability. The corrugated boards in our company are produced by hot pressing