The invention relates to a novel low profile additive (LPA) for uncured polyester resins and the resultant molding compositions. The low profile additive is the reaction product of an ethylene/alphaolefin copolymer with a carboxylic acid or anhydride, to thereby form a non-thermoplastic carboxyl modified polyolefin. The novel LPA is a remarkably effective dimensional stabilizer and has displayed the ability to achieve net expansion in a cured polyester resin molding composition.