special bipolar aluminum electrolytic capacitors designed for bipolar operation are available, and usually referred to as "non-polarized" or "bipolar" types. in these, the capacitors have two anode foils with full-thickness oxide layers connected in reverse polarity. on the alternate halves of the ac cycles, one of the oxides on the foil acts as a blocking dielectric, preventing reverse current from damaging the electrolyte of the other one. but these bipolar electrolytic capacitors are not adaptable for main ac applications instead of power capacitors with metallized polymer film or paper dielectric.