a continuous mixing vessel for polymer processing materials characterized in that the progress of the materials being mixed through the mixing volume is substantially vertical so as to permit natural subsidence of the materials , whereby mixture of the materials is caused by the effects of the different subsiding speeds of the materials and the gradient in the subsiding speed between the center and wall portions of the mixing vessel . horizontal agitators are preferably provided , but they must induce no vertical movement of the materials . a hot wind may be introduced into a lower portion of the mixing vessel and be exhausted from an upper portion of the mixing vessel after having dried the materials as it moves through them in counterflow .