an extrusion process is disclosed wherein coolant under pressure is directed against the outer surface of a thermoplastic material being forced through an extrusion orifice such that at least a portion of the coolant immediately vaporizes and the resultant heat of vaporization required for such action is taken from the material immediately contacting such . the coolant is introduced into an intermediate zone downstream from an initial extrusion zone and the interface between such zones is insulated so as to restrict conductive heat transfer between such zones immediately adjacent thereto so as to prevent possible freeze ups of said material in the initial extrusion zone .