Historically, nucleating agents have been used extensively to adjust the mechanical and optical properties of polymers and in particular polypropylene. Nucleating agents work by providing a surface on which crystal growth can commence and propagate. This improves the rate of crystallization and in some instances changes the size /shape of the crystals to produce novel properties such reduced cycle times, increased - flexural modulus, strength, heat distortion temperature and hardness. The issue of organic pigments partially nucleating polymers resulting in variation of crystallization rates, shrinkage, and higher rejection rates due to warpage is also overcome by the incorporation of nucleating agents. The addition of nucleating agents (also known as ‘Pigment Levelling’) will improve performance and reduce rejection rates in pigmented system (e.g. phthalo blue pigments).