Grooved barrel single screw extruders have been known for many years and are widely used in industry especially for high molecular weight thermoplastics respectively for the production of pipes, blown films or blow-molded parts. The grooves are classical designed with a tapered profile with a length of three to five times the screw diameter. In case of the so called HELIBAR® system, invented by Grünschloß, the inner wall of the feeding and the melting section are provided with tapered grooves. In case of the invented single screw extruder the grooves are not designed with a tapered profile. The diameter of the barrel at the end of the grooves corresponds to the diameter before the end of the grooves plus approx. twice times the groove depth. At the same time the outside screw diameter after the grooves equals the barrel inside diameter taking a necessary clearance into account. A larger volume at the end of the grooves is a result of this construction, and thus the risk of a pressure peak is reduced and the conveying capacity is increased. Due to the extended grooves without compression the mass throughput fraction of the grooves as well as the total mass throughput can be increased. Melt pumping of the melt conveying zone is more efficient due to the increased screw diameter after the grooves. This enables also the usage of sophisticated and frequently pressure consuming geometries like wave or energy transfer concepts. Low melt temperatures and high mass throughputs can be achieved with barrier screw concepts as a consequence of an observed melt cooling effect based on a solid conveying mechanism from the extended grooves into the melt channel. In summary the new grooved single screw extruder concept offers significant benefits not only compared to smoothed barrel extruders, but also towards classical grooved feed single screw extruders in terms of mass throughput, pressure build up capacity and melt temperature.