A non-isothermal, 3-D discrete particle simulation based on the discrete element method (DEM) was developed to simulate the solids-conveying zone and feed hopper of a single-screw extruder. The method considers each particle in a granular assembly as a separate entity that can interact with other particles or boundaries through collisions or lasting contacts. By using DEM to model the extrusion environment, a priori knowledge of the solids flow was not required in order to simulate the motion of a granular assembly with reasonable accuracy, allowing studies to be conducted in the absence of the solid plug assumption typical of classical solids-conveying models. In this paper, predicted results were limited to low levels of compaction in the solids assembly (i.e., no particle deformation), in order to understand the behavior of the polymer pellets in their most dynamic state. The results of the DEM model showed reasonably good agreement with experimental data, providing comparable bulk values like output nate, yet also demonstrating its ability to capture the dynamics of solids particle conveying. The model captured the inherent variability of extrusion such as the low-amplitude, high-frequency fluctuations referred to as "solids pulsing" and the recirculation of pellets in the feed throat. (C) 2004 Society of Plastics Engineers.