Homogeneous storable mixtures containing small quantities of a potassium halide, having a high mixed hydroxyl number or mixed hydroxyl/amine number and an average functionality of at least 2.0 are made by mixing (a) a polyoxyalkylene polyol and/or polyolamine and/or polyamine based on an alkyloxirane having a molecular weight of from 400 to 12,000 and (b) a low molecular weight polyol which is not completely miscible with (a) wherein these mixtures are reacted with a prepolymer or a polyisocyanate to produce shrink stable thermal break urethanes having good adhesion to substrate properties and wherein the use of such mixtures increases processing flexibility without detrimentally affecting the physical properties of the thermal break urethanes produced.