The core spun yarn is generally a yarn made of synthetic fiber filaments with good strength and elasticity as the core yarn and twisted together with short fibers such as cotton, wool and viscose. The yarn has the excellent properties of filament yarn and short staple fiber. The more common yarns are polyster-cotton yarns, which use polyster filament as the core and are coated cotton fibers. The knitted fabrics or jeans material made of this yarn can be stretched freely and comfortable to fit.