Abstract: A process and a device for producing filtration-active fibers is described. An aqueous suspension is produced from a homopolymer of polyacrylonitrile, polyamide or cellulose acetate and the suspension is heated in a tank to a temperature T which is at least 60° above the boiling point of the water and at least 30° C. below the softening temperature of the polymer. The at least plasticized polymer mass which has been obtained in this way is discharged through at least one nozzle means at least using the autogenous pressure of superheated water. The device calls for that the suspension is prepared in a storage tank, that a mixing tank is connected to the storage tank and is made for heating an aqueous polymer suspension under pressure, and that furthermore there is a nozzle means for discharge of the plasticized polymer mass located at the output of the mixing tank.