Blowing agents in polymer foam processing systems

A method comprising:

• providing a hopper of a polymer foam processing system;
• supplying polymeric material to the hopper;
• supplying chemical blowing agent to the polymeric material in the polymer foam processing system;
• supplying physical blowing agent comprising nitrogen to the polymeric material in the polymer foam processing system;
• conveying a mixture of the polymeric material, the chemical blowing agent and the physical blowing agent comprising nitrogen in a downstream direction in the extruder, wherein the nitrogen is present in an amount between 0.025 and 1.50 weight percent based on the total weight of polymeric material;
• decomposing the chemical blowing agent to form carbon dioxide that is present in an amount between 0.2 and 3.0 weight percent chemical blowing agent;
• accumulating a shot of the mixture of polymeric material and blowing agent;
• and
• injecting the shot into a blow mold to form a blow-molded polymeric foam article.