Polyesters and polyol formulations comprising polyesters used in the preparation of polyisocyanurate rigid foams with improved green strength properties are provided. In some embodiments, a polyester which is the reaction product of (a) an aromatic component comprising 80 mole percent or greater of terephthalic acid, (b) at least one polyether polyol having a nominal functionality of 2, a molecular weight of 150 to 1,000 and a polyoxyethylene content of at least 70% by weight of the polyether polyol, (c) at least one glycol different than (b) having a nominal functionality of 2 and a molecular weight from 60 to 250, and (d) at least one polyol having a molecular weight of 60 to 250 and a nominal functionality of at least 3, wherein (a), (b), (c), and (d) are present in the reaction on a percent weight basis of 20 to 60 weight percent of (a), 20 to 50 weight percent of (b), 10 to 30 weight percent of (c), and 5 to 20 weight percent of (d) is provided.