PURPOSE: To obtain titled foam having excellent heat resistance, etc., by mixing a styrene resin with a volatile organic compound as a blowing agent, a bromine- containing organic compound as a flame retardant and lead stearate and extruding the mixture through an extruder.

CONSTITUTION: 100pts.wt. styrene resin is mixed with 1W30pts.wt. volatile organic compound having a b.p. lower than the softening point of the styrene resin, e.g., propane, methyl chloride, acetone, or methyl acetate, as a blowing agent and 1W 2pts.wt. bromine-containing organic solid compound, e.g., hexabromocyclododecane or 2,2-bis(4-allyloxy-3,5-dibromphenyl)-propane, as a flame retardant and 0.1W 2pts.wt. lead stearate. Then, the resulting mixture is fed to an extruder and extruded through a die to obtain titled resin foam.