There are now nine of the largest tandem foam extruders on the market running polystyrene foam blown with CO2 or nitrogen gas. All located in Europe, they are recently introduced ZE 110/KE 400 units from Berstorff GmbH in Germany, parent of Berstorff Corp., Florence, Ky. These machines are guaranteed for 3300 lb/hr, but can actually produce close to 4000 lb/hr, Berstorff says. Now Berstorff is designing an even larger model for 4400 lb/hr, which it expects to build next year. (The highest throughput with CO2 blowing from competitors is around 2200 lb/hr.) The machines have been selling in Europe since 2001, when R22 and R142b fluorocarbon blowing agents were banned. The U.S. market has until 2010 to make the switch. PS foam with CO2 reportedly is a little denser (37 vs. 35 g/cc), a little higher in compressive strength, and a little poorer in insulating value than foams with R22/R142b.