A process for extrusion of polymer comprising feeding a polymer feedstock to the feed port of an extruder, said extruder comprising: (i) two or more barrel sections (la, 1b, 1c) arranged sequentially from: (a) an upstream feed barrel section (la) to which polymer feedstock to be extruded is fed, the upstream feed barrel section (la) having two screws each having a diameter of X; to (b) a downstream barrel section (lc) from which melted polymer is passed to a die and extruded; and (ii) one or more feed ports for feeding polymer feedstock to be extruded into the extruder at its upstream end, wherein (a) the polymer feedstock is a polymer of ethylene or propylene, being either homopolymers thereof or copolymers thereof with another comonomer, and is in the form of a powder having a flowability ratio of less than 6, said flowability ratio of the polymer powder being measured using the instantaneous shear test described in ASTM D 6773-02 at a consolidation pressure of 2000 Pa and at a temperature that is equal to the temperature of the polymer powder at the feed port during the extrusion process, (b) the diameter of the screws in the feed port barrel section is 200 mm or greater, and (c) the total area of the one or more feed ports through which polymer feedstock is introduced is greater than 5*X 2. (i) two or more barrel sections (la, 1b, 1c) arranged sequentially from: (a) an upstream feed barrel section (la) to which polymer feedstock to be extruded is fed, the upstream feed barrel section (la) having two screws each having a diameter of X; to (b) a downstream barrel section (lc) from which melted polymer is passed to a die and extruded; and (a) an upstream feed barrel section (la) to which polymer feedstock to be extruded is fed, the upstream feed barrel section (la) having two screws each having a diameter of X; to (b) a downstream barrel section (lc) from which melted polymer is passed to a die and extruded; and (ii) one or more feed ports for feeding polymer feedstock to be extruded into the extruder at its upstream end, wherein (a) the polymer feedstock is a polymer of ethylene or propylene, being either homopolymers thereof or copolymers thereof with another comonomer, and is in the form of a powder having a flowability ratio of less than 6, said flowability ratio of the polymer powder being measured using the instantaneous shear test described in ASTM D 6773-02 at a consolidation pressure of 2000 Pa and at a temperature that is equal to the temperature of the polymer powder at the feed port during the extrusion process, (b) the diameter of the screws in the feed port barrel section is 200 mm or greater, and (c) the total area of the one or more feed ports through which polymer feedstock is introduced is greater than 5*X 2. (a) the polymer feedstock is a polymer of ethylene or propylene, being either homopolymers thereof or copolymers thereof with another comonomer, and is in the form of a powder having a flowability ratio of less than 6, said flowability ratio of the polymer powder being measured using the instantaneous shear test described in ASTM D 6773-02 at a consolidation pressure of 2000 Pa and at a temperature that is equal to the temperature of the polymer powder at the feed port during the extrusion process, (b) the diameter of the screws in the feed port barrel section is 200 mm or greater, and (c) the total area of the one or more feed ports through which polymer feedstock is introduced is greater than 5*X 2.