A composition comprising

(a1) a polyether polyol,

(a2) a polyolefin polyol and

(a3) a polyester polyol obtainable by epoxidation of an unsaturated fatty acid ester and subsequent ring-opening reaction with a compound containing active hydrogen, can be used for the preparation of PUR foam which distinguishes by low-temperature flexibility and low dielectric loss and is suitable for filling the gap between the condenser core and the outer composite or porcelain insulator in the manufacture of resin impregnated paper (RIP) bushings.

A composition of the formulae MZAORS.sub.nR.sup.1F.sup.1.sub.mOAZ.sup.1M.sup.1, wherein O and S have their normal meaning of oxygen and sulfur, n is at least 2 and not more than 8, F.sup.1 is of the formula OAORS.sub.nR.sup.1, m is at least 1, Z and Z.sup.1 are the same or different and are oxy or amino, M and M.sup.1 are the same or different and are hydrogen or an organic substituent, R and R.sup.1 are the same or different and are organic divalent radicals, each having from 2 to 20 carbon atoms, and A is the residue of a dicarboxylic acid of from 2 to 40 carbon atoms.

Provided is a method for producing a one-component moisture-curing polyurethane composition, the method comprising: a mixing step in which a liquid component (A) containing a polyol compound is mixed with a powder component (B) containing a filler so as to obtain a paste-like mixture of the liquid component (A) and the powder component (B); a dehydration step in which, following the mixing step, at least a portion of the residual moisture in the paste-like mixture is removed; a prepolymer generation step in which a polyisocyanate compound (C) is mixed with the paste-like mixture following the dehydration step so as to obtain a mixture containing a urethane prepolymer generated by a reaction between the polyisocyanate compound (C) and the polyol compound in the paste-like mixture; and a composition generation step in which the mixture is mixed with an aliphatic isocyanate compound (D) so as to obtain a one-component moisture-curing polyurethane composition.