A thermoplastic composition comprising a) a molding resin comprising (a-1) a poly(trimethylene terephthalate) homopolymer or copolymer; (a-2) optionally, 0.1 to 20 weight % of one or more organic additives selected from the group consisting of lubricants, flow modifiers, plasticizers, heat stabilizers, antioxidants, dyes, pigments, and UV stabilizers; (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 C 3 to C 8 carboxylic acid repeat units, and each ionomer and acid copolymer having: a weight %, W; a weight fraction of C 3 to C 8 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 said 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 14; wherein said ACF is defined by the formula: ACF = ∑ a − i W ⋅ Z ⋅ N a − i W ⋅ N a − i ⋅ 100 / ∑ a − i W a − i and, b) 0 to 50 wt % of one or more fillers, based on the total weight of the thermoplastic composition. a) a molding resin comprising (a-1) a poly(trimethylene terephthalate) homopolymer or copolymer; (a-2) optionally, 0.1 to 20 weight % of one or more organic additives selected from the group consisting of lubricants, flow modifiers, plasticizers, heat stabilizers, antioxidants, dyes, pigments, and UV stabilizers; (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 C 3 to C 8 carboxylic acid repeat units, and each ionomer and acid copolymer having: a weight %, W; a weight fraction of C 3 to C 8 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 said 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 14; wherein said ACF is defined by the formula: ACF = ∑ a − i W ⋅ Z ⋅ N a − i W ⋅ N a − i ⋅ 100 / ∑ a − i W a − i and, (a-1) a poly(trimethylene terephthalate) homopolymer or copolymer; (a-2) optionally, 0.1 to 20 weight % of one or more organic additives selected from the group consisting of lubricants, flow modifiers, plasticizers, heat stabilizers, antioxidants, dyes, pigments, and UV stabilizers; (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 C 3 to C 8 carboxylic acid repeat units, and each ionomer and acid copolymer having: a weight %, W; a weight fraction of C 3 to C 8 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 said 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 14; wherein said ACF is defined by the formula: ACF = ∑ a − i W ⋅ Z ⋅ N a − i W ⋅ N a − i ⋅ 100 / ∑ a − i W a − i and, a weight %, W; a weight fraction of C 3 to C 8 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 said 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 14; wherein said ACF is defined by the formula: ACF = ∑ a − i W ⋅ Z ⋅ N a − i W ⋅ N a − i ⋅ 100 / ∑ a − i W a − i and, b) 0 to 50 wt % of one or more fillers, based on the total weight of the thermoplastic composition.