Successive sections of a strand material are advanced along a predetermined path into an entrance end of, through, and then out of a laterally closed chamber. The entrance end of the chamber is in communication with the air of the ambient atmosphere. High velocity jet streams of treating material are directed into the chamber toward oblique converging engagement with the successive sections of the strand material. Substantial components of the velocities of the jet streams are in the direction of travel of the strand material. The minimum cross-sectional area of the passages of the chamber through which the streams are directed and the strand material travels are substantially greater than that of the strand material. The velocity of the jet streams and the geometrical relationship of passages of the chamber through which the strand material and the jet streams pass and the pressure of the air are such as to create pressure differentials sufficient to cause air to be drawn into the entrance of the chamber at a volumetric flow which is substantially greater than that of the treating material. The air is mixed with the treating material to produce a vapor mixture which moves through the chamber along the path of the strand material to treat the strand material.
