A multiple-hole die for the production of single large blocks of polystyrene foam with carbon dioxide as blowing agent was developed. First, single-hole die experiments were carried out with different hole sizes (2.0, 1.0, and 0.50 mm). Using these single-hole dies dimensionally-stable foam was produced with a density of 31 kg m(-3) and an open cell structure. Next, the hole diameter and hole distances for a newly constructed multiple-hole die were chosen on basis of the radial expansion in the single-hole die experiments. Tests with the multiple-hole die showed that the seven strings could melt together forming one large string with a diameter of about 20 mm and a density of 50 kg m(-3). Therefore, the concept of using a multiple-hole die for producing single large blocks of polystyrene was proven. However, larger block sizes were not possible because of the limited capabilities of the extruder. POLYM. ENG. SCI., 51:2328-2334, 2011. (C) 2011 Society of Plastics Engineers