Abstract: A fluid, insulating composition, useful for casting around conductors, is made from a liquid, polymerizable organic resin system, and a liquid, non-polymerizable organopolysiloxane dielectric filler partially soluble in the organic resin system and having the structural formula:(R).sub.3 --Si[OSi(R).sub.2)].sub.n OSi(R).sub.3,where n=0 to about 10, and each R group is selected from H, alkyl having from 1 to 6 carbons, and phenyl, where the dielectric is added in an amount such that, upon polymerization of the organic resin system to form a resin matrix containing dielectric filler, the dielectric will flow or diffuse through the resin matrix into cavities or voids in or bordering the composition or near any insulated conductors or other insulated articles.