Alkenyl aromatic foam with low solubility hydrofluorocarbon

A process for preparing extruded polymer foam comprising the steps:

• (a) preparing a foamable mixture of a thermoplastic polymer composition and blowing agent composition at a mixing temperature and mixing pressure in a range of 13.2 to 19.0 megaPascals;
• (b) cooling the foamable mixture to a foaming temperature;
• and
• (c) exposing the foamable mixture to an environment at a lower pressure than the mixing pressure and allowing the foamable mixture to expand into a polymer foam;
• wherein, more than 95 wt % of the thermoplastic polymer composition is one or more styrene-acrylonitrile copolymer and wherein 1,1,1,2-tetrafluoroethane is present at a concentration of more than 30 weight-percent based on total blowing agent composition weight and at least eight weight-percent and 12 weight-percent or less based on thermoplastic polymer composition weight and wherein the polymer foam of step (c) is an extruded polymer foam comprising a thermoplastic polymer composition defining a plurality of cells therein, characterized by:
• (i) more than 95 weght-percent of the thermoplastic polymer composition is a styrene-acrylonitrile copolymer;
• (ii) having less than 30% open cell content according to ASTM method D6226-05;
• (iii) having a density of 48 kilograms per cubic meter or less according to ISO method 845-85;
• and (iv) containing at least eight weight-percent and 12 weight-percent or less, based on total foam weight, of 1,1,1,2-tetrafluoroethane.