Carbon black-containing bimodal foam structures and process for making

A process for making a closed-cell, insulative styrenic polymer foam structure having relatively larger primary cells with an average cell size range of 0.05 to 1.2 millimeters and relatively smaller secondary cells ranging in cell size from about 5 percent to about 50 percent of the average cell size of the primary cells, comprising:

• a) heating a styrenic polymer material comprising greater than 50 percent by weight of styrenic monomeric units to form a melt polymer material;
• b) incorporating into the melt polymer material an amount of carbon black sufficient to reduce the thermal conductivity of the foam structure below that of a corresponding structure without carbon black;
• c) incorporating into the melt polymer material at an elevated pressure a blowing agent comprising an amount of water sufficient to form a foamable gel expandable to form the foam structure.
• d) expanding the foamable gel at a reduced pressure to form the foam structure.