Abstract: The shrinkage of a thermosettable composition comprising an unsaturated polyester and a vinyl monomer capable of cross-linking the polyester is reduced during cure by the addition to the composition of an alkylene oxide polymer which is soluble in the thermosettable composition but which is substantially less soluble in the cured thermoset composition.

Abstract: Low shrink and low profile reinforced plastic systems are prepared from vinyl ester resins by incorporating therein an additive having the formula: ##STR1## WHEREIN R.sub.1 and R.sub.2 are hydrogen, methyl or ethyl with the provision that, if either R.sub.1 or R.sub.2 is hydrogen, the other is methyl or ethyl, n and m are whole numbers such that said additive is soluble in said resin when uncured and insoluble in said resin when cured; and B is the residue of a hydroxyl containing initiating compound. Typical of such compounds are water, ethylene glycol, glycerine and phenol. The value of p is equal to or less than the number of hydroxyls in the initiating compound.