the polymer hcfc 142b or 4 to 12 of hfc 134a with 0 to 3 ethanol alternatively 3 to 8 carbon dioxide with 0 to 4 lower alcohol which include ethanol methanol propanol isopropanol and butanol optional additives which may be incorporated in the extruded foam product include additionally infrared attenuating agents plasticizers flame retardant chemicals pigments elastomers extrusion aids antioxidants fillers antistatic agents uv absorbers etc these optional additives may be included in any amount to obtain desired characteristics of the foamable gel or resultant extruded foam products preferably optional additives are added to the resin mixture but may be added in alternative ways to the extruded foam manufacture process the rigid polystyrene foam has improved thermal insulating properties unlike most infrared attenuating agents iaas which increase polymer viscosity during extruding process asphalt decreases the polymer viscosity the flow rate of melted polymer through an orifice described as melt flow index or simply melt index mi tested according to iso 1133 1977 e the melt flow index can be used as a characteristic parameter related to molecular weight and viscosity of the polymer fig1 a small amount of asphalt demonstrates the benefit of improved thermal insulation value r inch typically the amount of asphalt ranges from about 0 1 to 15 preferably from 0 5 to 3 by weight on the base polymer the asphalt may be any petroleum derived asphalt with a softening point from about 105 to about 155 u00b0 c one particularly suitable asphalt for use in the rigid foams of the present invention is granulated asphalt such as su 7606 owens corning trumbull ohio usa with a particle size around 2 4 mm 8 mesh and softening point of about 123 u00b0 c the granulated asphalt can be added directly into the molten polymer during.