A polymeric melt composition includes a polymeric material and a nucleating agent additive composition. The nucleating agent additive composition includes (a) at least one carbonate or bicarbonate, (b) at least one organic acid or its salt, and (c) at least one desiccant. The polymeric material is unfoamed by the additive composition. The additive composition can induce polymer nucleation, such that the rate of production for polymeric articles made by melt forming processes such as injection molding can be improved, even when the carbonate or bicarbonate is present at only very low levels in the polymeric melt composition from which the polymeric articles are shaped.