A foam extrusion assembly having a melt region which receives and melts a plurality of material pellets, an agent addition assembly which adds a foaming agent to the melted material pellets, and a mixing assembly which substantially mixes the melted material pellets and the foaming agent with one another. The mixing assembly includes a generally elongate barrel through which the melted material pellets and the foaming agent are urged generally from an inlet to an outlet of the barrel. Furthermore, the mixing assembly includes a mixing plug disposed in the barrel and structured to define at least two sequentially disposed flow passages along a length thereof, the flow passages, which are structured and disposed to receive the melted material pellets and the foaming agent therethrough so as to define a flow path past the mixing plug, each have at least one substantially small transverse dimension so as to restrict amounts of the melted material pellets and the foaming agent which enter the flow passage at one time, and are generally short in length so as to minimize a duration of a flow restriction at the flow passages. As a result a well homogenized extrusion mixture is provided and is passed at an extrusion temperature through a die which forms the extruded foam product.