Abstract: The invention relates to a device for joining together at least two material flows in a laminar coextrusion machine comprising at least two extruders, more precisely as many extruders as layers of different materials used, a device for joining together the flows coming from the extruders into a so-called global flow, said device being also called a distribution box, and an extrusion head supplied by the global flow. The joining device includes a main channel wherein open annexed channels called supply channels convey the different material flows coming from the extruders, the channels being provided with means for restricting the flow passage cross-section. The supply channel connecting each extruder to the main channel is at least partially in the form of a cylindrical plug valve having means which transform a cylindrical rod into a planar sheet.