An extrusion head for the manufacture of tubes including at least one layer of expanded plastic by extruding a stream of molten plastic containing a blowing agent through an annular passage cross section made in the extrusion head. The stream of molten plastic containing the blowing agent spreads out circumferentially and welds itself to itself by the recombining of the two stream fronts. The extrusion head is equipped with a special-purpose thermal regulation device allowing the molten plastic containing the blowing agent to be heated or cooled after the stream fronts have recombined.