Disclosed is a thermoplastic composition including a molding resin including (a-1) a poly(trimethylene terephthalate) resin, (a-2) 0 to 20 weight % of one or more organic additives; and (a-3) 0.1 to 4 weight % of one or more ionomer polymers or a combination of one or more ionomer polymers and acid copolymers; said ionomer polymers and acid copolymers having C3 to C8 carboxylic acid repeat units, and each ionomer and acid copolymer having: a weight %, W; a weight fraction of C3 to C8 carboxylic acid repeat units, Z, based on the weight of each ionomer or acid copolymer; and a neutralization ratio, N, equal to any value from 0 to 1.0; wherein said neutralization ratio N is the mol fraction of the carboxylic acid repeat units neutralized as an alkali metal salt, based on the total carboxylic acid repeat units in said ionomer and acid copolymers; and said each ionomer and acid polymer wt % W is based on the weight of components (a-1), (a-2) and (a-3); and said molding resin has an alkali carboxylate factor, ACF, of 4 to about 14; wherein said ACF is defined by the formula (I): ACF=Σa-i[(W·Z·N)a-i(W·N)a-i·100/Σa-i(W)a-i]  (I).