A process for preparing an alkenyl aromatic polymer foam comprising the following steps in order: (a) providing a foamable composition comprising a polymer and a blowing agent, wherein more than 50 weight-percent of the polymer consists of one or more alkenyl aromatic polymer; and (b) expanding the foamable composition into a polymer foam; wherein the blowing agent consists of: one or more fluorinated alkene at a concentration of 0.03 moles or more and 0.3 moles or less per 100 grams of polymer, the fluorinated alkene being selected from a group consisting of: 2-fluoropropene, 1-fluoropropene; 1,1-difluoropropene; 3,3-difluoropropene; 3,3,3-trifluoropropene; 2,3,3-trifluoropropene; 1,3,3,3-tetrafluoropropene; 1,1,3,3-tetrafluoropropene; 1,2,3,3,3-pentafluoropropene; 4,4,4-trifluoro-1-butene; 3,4,4,4-tetrafluoro-1-butene; 1,1,3,3,3-pentafluoro-2-methyl-1-propene; octafluoro-1-butene; octafluoro-2-butene; 2,3,3,4,4,4-hexafluoro-1-butene; 1,1,1,4,4,4-hexafluoro-2-butene; 1,1,1,2,4,4,4-heptafluoro-2-butene; and 1,1,1-trifluoro-2-butene; and one or more blowing agent selected from a group consisting of alcohols having from one to five carbons, water and carbon dioxide; wherein more than 50 weight-percent of the blowing agent consists of one or more of the fluorinated alkenes; and wherein the alkenyl aromatic polymer foam comprises a polymer matrix containing one or more polymer and defining a plurality of cells having an average cell size, wherein the alkenyl aromatic polymer foam has: (i) an average cell size according to ASTM method D-3576-04 that is in a range of 0.02 and 5 mm; (ii) a density of 64 kg/m 3 or less according to ISO method 845-85; (iii) an open cell content less than 30% according to ASTM method D6226-05; and iv) a cell size variation of 30% or less as defined in the "Terms" section of the description. (a) providing a foamable composition comprising a polymer and a blowing agent, wherein more than 50 weight-percent of the polymer consists of one or more alkenyl aromatic polymer; and (b) expanding the foamable composition into a polymer foam; one or more fluorinated alkene at a concentration of 0.03 moles or more and 0.3 moles or less per 100 grams of polymer, the fluorinated alkene being selected from a group consisting of: 2-fluoropropene, 1-fluoropropene; 1,1-difluoropropene; 3,3-difluoropropene; 3,3,3-trifluoropropene; 2,3,3-trifluoropropene; 1,3,3,3-tetrafluoropropene; 1,1,3,3-tetrafluoropropene; 1,2,3,3,3-pentafluoropropene; 4,4,4-trifluoro-1-butene; 3,4,4,4-tetrafluoro-1-butene; 1,1,3,3,3-pentafluoro-2-methyl-1-propene; octafluoro-1-butene; octafluoro-2-butene; 2,3,3,4,4,4-hexafluoro-1-butene; 1,1,1,4,4,4-hexafluoro-2-butene; 1,1,1,2,4,4,4-heptafluoro-2-butene; and 1,1,1-trifluoro-2-butene; and one or more blowing agent selected from a group consisting of alcohols having from one to five carbons, water and carbon dioxide; wherein more than 50 weight-percent of the blowing agent consists of one or more of the fluorinated alkenes; and wherein the alkenyl aromatic polymer foam comprises a polymer matrix containing one or more polymer and defining a plurality of cells having an average cell size, wherein the alkenyl aromatic polymer foam has: (i) an average cell size according to ASTM method D-3576-04 that is in a range of 0.02 and 5 mm; (ii) a density of 64 kg/m 3 or less according to ISO method 845-85; (iii) an open cell content less than 30% according to ASTM method D6226-05; and iv) a cell size variation of 30% or less as defined in the "Terms" section of the description. (i) an average cell size according to ASTM method D-3576-04 that is in a range of 0.02 and 5 mm; (ii) a density of 64 kg/m 3 or less according to ISO method 845-85; (iii) an open cell content less than 30% according to ASTM method D6226-05; and iv) a cell size variation of 30% or less as defined in the "Terms" section of the description. <EOS>