Extrusion process of polystyrene in the molten state

A process for preparing a polymeric foam, comprising forming a pressurized melt containing a molten styrenic polymer, 0.4 to 100 parts by weight, per 100 parts by weight of the styrenic polymer, of a brominated styrene-butadiene polymer and 1 , 1 to 1.70 moles of a mixture of blowing agent per kilogram of styrenic polymer, and passing the melt through an opening in a low pressure zone, where the blowing agent expands and the polymer cools and solidifies to form a foam, where the blowing agent mixture includes 0.65 to 0.9 moles of carbon dioxide per kilogram of styrenic polymer, 0.25 to 0.45 moles of ethanol per kilogram of styrenic polymer, 0 , 1 to 0.3 moles of a C4-C5 hydrocarbon per kilogram of styrenic polymer and 0.1 to 0.3 moles of water per kilogram of styrenic polymer, where the average foam cell size is between 0.25 mm and 1 mm, according to ASTM D3576.