A process for preparing extruded polymeric foam comprising providing a foamable polymer composition at an initial pressure and temperature in an extruder and then extruding the foamable polymer composition into an atmosphere of lower pressure than the initial pressure and allowing the foamable polymer composition to expand into polymeric foam; wherein the foamable polymer composition comprises: a. a thermoplastic polymer matrix comprising a polymer component that contains all the polymers in the thermoplastic polymer matrix; b. a blowing agent composition dispersed within the thermoplastic polymer matrix, the blowing agent composition comprising 3 to 5 weight-percent carbon dioxide, up to 5 wt% alcohol having 2-3 carbons, up to 0.7 wt% water and up to 2.5 weight-percent iso-butane; wherein the blowing agent comprises at least 0.1 weight-percent of water and/or alcohol having 2-3 carbons; c. two weight-percent or more and five weight-percent or less of an infrared attenuating agent dispersed within the thermoplastic polymer matrix, the infrared attenuating agent selected from a group consisting of carbon black having an average particle size of 100-700 nanometers and petcokes; d. 2.5 to 3.5 weight-percent of a brominated flame retardant dispersed within the thermoplastic polymer matrix, wherein the brominated flame retardant is selected from hexabromocyclododecane (HBCD), brominated polystyrene, brominated butadiene and brominated styrene-butadiene copolymers; and e. at least 0.1 weight-percent of epoxy stabilizer dispersed within the polymer matrix; where all weight-percents are relative to total polymer component weight, wherein at least 50 weight-percent of the polymer component is alkenyl aromatic polymer and wherein the resulting polymeric foam is characterized by having a density in a range of 30 to 37 kilograms per cubic meter, a unimodal cell size distribution with an average cell size in a range of greater than 0.15 and 0.4 millimeters or less, a thermal conductivity in a range of 28 to 35 milliwatts per meter*Kelvin and that passes the German B2 fire test. a. a thermoplastic polymer matrix comprising a polymer component that contains all the polymers in the thermoplastic polymer matrix; b. a blowing agent composition dispersed within the thermoplastic polymer matrix, the blowing agent composition comprising 3 to 5 weight-percent carbon dioxide, up to 5 wt% alcohol having 2-3 carbons, up to 0.7 wt% water and up to 2.5 weight-percent iso-butane; wherein the blowing agent comprises at least 0.1 weight-percent of water and/or alcohol having 2-3 carbons; c. two weight-percent or more and five weight-percent or less of an infrared attenuating agent dispersed within the thermoplastic polymer matrix, the infrared attenuating agent selected from a group consisting of carbon black having an average particle size of 100-700 nanometers and petcokes; d. 2.5 to 3.5 weight-percent of a brominated flame retardant dispersed within the thermoplastic polymer matrix, wherein the brominated flame retardant is selected from hexabromocyclododecane (HBCD), brominated polystyrene, brominated butadiene and brominated styrene-butadiene copolymers; and e. at least 0.1 weight-percent of epoxy stabilizer dispersed within the polymer matrix;