A method of manufacturing an extruded part having an exterior shell and a core foam material. The method includes extruding the exterior shell from an extrusion die, and reaction injection molding the core foam material within an interior of the exterior shell using a distribution block having a plurality of orifices configured to inject the core foam material within the interior of the exterior shell. The orifices are configured to evenly distribute the core foam material throughout the interior of the exterior shell. the method can be used to form an exterior shell having a plurality of internal chambers, where the orifices of the distribution block are configured to inject core foam material within the plurality of internal chambers.