Process and apparatus for spinning fibers into a yarn in a yarn forming zone in the gap between air permeable surfaces of two rollers or on a single, air permeable roller surface while drawing a current of air adjacent said zone through said surface or surfaces by suction means, a feed channel with a narrow mouth adjacent the yarn forming zone for feeding an air stream and individual, separated fibers therein to the yarn forming zone from a carding roller rotating in a carding chamber to which a sliver or tow of fibers is fed, a casing about the rollers and the mouth of the channel with means for maintaining a desired subatmospheric to superatmospheric pressure in the casing and especially in the free flight interval of the fibers from the channel mouth to the yarn forming zone, a pressurizable casing about the carding unit and at least one air passage from the casing to the carding chamber, and using sequential, cascade-type, pressure decreases in the carding chamber, the feed channel, the free flight interval of the fibers at the yarn producing zone, and the suction means to attain optimum conditions for producing uniform and high strength yarns.