Yarn structural properties change according to raw material type and spinning parameters, influencing fabric air permeability. Combinations of polyester (staple and filament) core and sheath, and viscose sheath, friction-spun yarns were produced. Raw material type, spinning-drum speed, air-suction pressure, and core/sheath ratio production parameters were measured. The fabric air permeability increased when coarse fibers were used as a raw material in friction-spun core yarn, when fabrics were knitted from filament core/staple sheath friction-spun yarns, and at higher core/sheath ratios. Fabric air permeability generally decreased at higher spinning drum speeds in friction core-yarn spinning. The effects of air-suction pressure and use of filament fibers in the core part of the yarn on air permeability were also studied.