Production of polystyrene foam panels by using an extruder, wherein a liquid blowing agent is injected into molten polystyrene in the extruder, the blowing agent is blended into the melt and the melt is homogenised, the melt, loaded with blowing agent, is discharged through a die of the extruder into a calibrator, in which the melt foams up and partially cools down, wherein the interior of the calibrator has a rectangular cross section, such that an extruded melt strand exits out of the calibrator, wherein melt strand is cut to length into panels, wherein a blowing agent is used that possesses at least partially partly fluorinated hydrocarbon molecules containing at least three carbon atoms, wherein the blowing agent is at least partially selected from the following group of blowing agents - HFO 1234ze - HFO1343zf - HFO1234yf and the panels are fully surface coated with a barrier film that forms at least a diffusion inhibitor for the blowing agent, wherein a) the extruded strand is treated on the broad sides, then the treated broad sides are coated with barrier film, the narrow sides are then treated and coated with barrier film, the extruded strand, coated on all sides, is then cut to length into panels, finally, the still uncoated narrow sides of the panel are coated with barrier film b) the extruded strand is treated on all sides and both broad sides of the extruded strands are coated with a barrier film that after coating protrudes over both edges of the extruded strand, the protruding film edge of one barrier film is then folded back to partially coat the narrow sides of the extruded strand, the protruding film edge of the other barrier film is then folded back to further coat the narrow sides of the extruded strand, wherein the folded-back film edges overlap on the narrow sides, the extruded strand, coated on all sides, is then cut to length into panels, finally, the still uncoated narrow sides of the panel are coated with barrier film, or c) the extruded strand is treated on all sides and both broad sides of the extruded strand are coated with a barrier film, the narrow sides of the extruded strand are then coated with barrier film, wherein the barrier film on the narrow sides protrudes over and under the extruded strand;subsequently the protruding film edges are folded back over the film on the broad sides, the extruded strand, coated on all sides, is then cut to length into panels, finally, the still uncoated narrow sides of the panel are coated with barrier film. - HFO 1234ze - HFO1343zf - HFO1234yf a) the extruded strand is treated on the broad sides, then the treated broad sides are coated with barrier film, the narrow sides are then treated and coated with barrier film, the extruded strand, coated on all sides, is then cut to length into panels, finally, the still uncoated narrow sides of the panel are coated with barrier film b) the extruded strand is treated on all sides and both broad sides of the extruded strands are coated with a barrier film that after coating protrudes over both edges of the extruded strand, the protruding film edge of one barrier film is then folded back to partially coat the narrow sides of the extruded strand, the protruding film edge of the other barrier film is then folded back to further coat the narrow sides of the extruded strand, wherein the folded-back film edges overlap on the narrow sides, the extruded strand, coated on all sides, is then cut to length into panels, finally, the still uncoated narrow sides of the panel are coated with barrier film, or c) the extruded strand is treated on all sides and both broad sides of the extruded strand are coated with a barrier film, the narrow sides of the extruded strand are then coated with barrier film, wherein the barrier film on the narrow sides protrudes over and under the extruded strand;subsequently the protruding film edges are folded back over the film on the broad sides, the extruded strand, coated on all sides, is then cut to length into panels, finally, the still uncoated narrow sides of the panel are coated with barrier film.