Sateen is a fabric made using a satin weave structure but made with spun yarns instead of filament.
The sheen and softer feel of sateen is produced through the satin weave structure. Warp yarns are floated over weft yarns, for example four over and one under. (In a weft-faced satin or sateen, the weft yarns are floated over the warp yarns.) Standard plain weaves use a one-over, one-under structure. The long floats produce a surface that is smooth to the touch and reduces light scattering to increase shine. This weave structure is more susceptible to wear than other weaves.
In modern times cheaper rayon is often substituted for cotton. Better qualities are mercerized to give a higher sheen. Some are only calendered to produce the sheen, but this disappears with washing.