The process of foaming a polyolefin, e.g., polyethylene, composition using as a nucleator a combination an azodicarbonamide (ADCA) and a fluororesin at a ADCA: fluororesin weight ratio of 60:40 to 20:80. The synergic effect between these two nucleating agents results in a higher nuclei density and a foamed product with a smaller cell size as compared to processes using and products produced by the use of neat PTFE or neat ADCA alone as the nucleating agent.