An extrusion facility (10) includes an extrusion screw (12), capable of providing a heat-softened viscous plastic material, and an extrusion (14). The extrusion head includes an annular chamber (24) that is capable of receiving viscous plastic material. The viscous plastic material, provided by the extrusion screw, has, at a constant temperature, a viscosity variable from a value μi at a constant value μcst during a given period so that μcst>μi. A buffer chamber (16) between the extrusion screw (12) and the extrusion head (14) to store the viscous plastic material during the given period in order to enable the plastic material to reach the viscosity value μcst before being injected into the extrusion head (14).