Flexible bimodal foam structures

A process for making a closed-cell styrenic polymer foam structure comprising a foam having relatively larger primary cells with an average cell size range of about 0.05 to about 1.2 millimeters and PG,16 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, the primary and secondary cells constituting at least about 90 percent of the total volume of the foam structure, the primary and secondary cells having pinholes between 1 and 30 percent by number of the total number of primary and secondary 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 at an elevated pressure a blowing agent in liquid or gaseous form comprising at least about 3 weight percent water based upon the total weight of the blowing agent and at least about 0.3 parts per hundred parts of the styrenic polymer material by weight to form a foamable gel;
• c) cooling the foamable gel to a selected foaming temperature;
• and
• d) expanding the foamable gel at a reduced pressure to form the foam structure.