An insulating composition for use in high voltage devices is formed from a soft dielectric casting compound, such as a silicone gel, comprising ferroelectric particles such as barium titanate dispersed within it. Low levels of particles, from 1% to 20% by volume of the insulating composition, are highly effective yet do not cause excessive thickening of the soft dielectric casting compound when it is in its liquid state. The insulating composition is particularly effective for coating, enrobing or encapsulating alternating high voltage devices such as power electronics devices in order to prevent electrical discharge.