A process to recycle and/or formulate expandable plastic materials using a system comprising the following units in fluid communication with each other and in the following sequence: - an extruder unit - a mixer-heat exchanger unit the system further comprising a melt pump unit also in fluid communication with previous said units (10, 20), wherein the melt pump unit is located either upstream of the mixer-heat exchanger unit and downstream of the extruder unit OR the melt pump unit is located downstream of the mixer-heat exchanger unit, said process comprising the steps of: - melting a feedstream comprising an expandable plastic material containing a first expansion agent in the extruder unit to form a molten expandable plastic material, - cooling the molten expandable plastic material in the mixer-heat exchanger unit; - controlling the melt pressure of the molten expandable plastic material by means of the melt pump unit, and subsequently either: (i) granulation of the molten expandable plastic material by means of a granulation unit to form a granulated expandable plastic material, (ii) extrusion of the molten expandable plastic material by a die to a controlled reduced pressure, preferably atmospheric pressure, to yield an extruded, formed and expanded plastic material, OR (ii) injection molding of the molten expandable plastic material by means of an injection molding unit to form a molded expanded plastic article, wherein the expandable plastic material comprises at least 40%, more preferably 60%, even more preferably 90 % by weight, and most preferably essentially all of the feedstream, wherein the system does not have a degasification unit and the first expansion agent is not degassed during a melt processing in the system such that the first expansion agent is substantially contained in the granulated expandable plastic material or used to form either the extruded, formed and expanded plastic material or the molded expanded plastic article, wherein the system further comprises one or more static mixer unit(s) and an additional mixing of the molten expandable plastic material by means of the static mixer unit(s) is carried out, and wherein an melt filtration unit is present and a filtering of the molten expandable plastic material by means of the melt filtration unit to form a filtered molten expandable material is carried out prior to the granulation, extrusion, or injection molding. - an extruder unit - a mixer-heat exchanger unit - melting a feedstream comprising an expandable plastic material containing a first expansion agent in the extruder unit to form a molten expandable plastic material, - cooling the molten expandable plastic material in the mixer-heat exchanger unit; - controlling the melt pressure of the molten expandable plastic material by means of the melt pump unit, (i) granulation of the molten expandable plastic material by means of a granulation unit to form a granulated expandable plastic material, (ii) extrusion of the molten expandable plastic material by a die to a controlled reduced pressure, preferably atmospheric pressure, to yield an extruded, formed and expanded plastic material, OR (ii) injection molding of the molten expandable plastic material by means of an injection molding unit to form a molded expanded plastic article,