Disclosed are polymeric compositions with improved electrical breakdown strength. The polymeric compositions contain a poly-α-olefin and a voltage-stabilizing agent, which comprises an organic carboxylic ester comprising at least one aromatic ring and from 1 to 2 carboxylic alkyl ester substituents. Alternatively, the voltage-stabilizing agent can comprise trioctyl trimellitate. The present polymeric compositions exhibit improved electrical breakdown strength when applied as an insulating and/or shielding layer for power cables.