Provide a foamable polymer composition containing: (i) a thermoplastic polymer matrix and a blowing agent, (a) the thermoplastic polymer matrix containing a styrene-acrylonitrile copolymer having a weight-averaged molecular weight in a range of 90,000 to 150,000 and polymerized acrylonitrile concentration in a range of five to twenty weight-percent relative to total polymer matrix weight; and (ii) a blowing agent containing water, 1,1,1,2-tetrafluouroethane and at least one of difluoromethane and 1,1-difluoroethane; (b) cooling the foamable polymer composition to a foaming temperature; and (c) extruding the foamable polymer composition and allowing the blowing agent to expand the foamable polymer composition into a polymeric foam having an average vertical cell size in a range of 0.5 millimeters to 1.8 millimeters and a density in a range of 24 to 40 kilograms per cubic meter and a Normalized Roughness Quotient of 3.5 or less in a Milled Surface Test.
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