A ‘Set-in’ sleeve is set in the arm hole of a garment at or near the natural edges of the shoulder. This sleeve style is mostly used in suits, coats, blazers and shirts because it gives a professional and natural look. The set-in sleeves can either lie flat, as it does in a man’s suit and dress shirt, or be gathered to pucker and rise above the garment at the shoulder, as it might in a little girl’s dress. The armhole of the sleeve is slightly longer that the armhole of the body, this creates more volume in the sleeve cap for your shoulder and upper arm.
The ‘set-in’ sleeves are larger than the armhole opening which makes it easier to fit the garment over the arm. the large opening also facilitates movement at the shoulder. The extent to which the top of the sleeve is larger than the armhole determines how high the sleeve rises above the garment, if at all. In any case, the top of the sleeve is gathered with stitches that are used to pull the fabric into small, evenly distributed puckers which allow the top of the sleeve to fit exactly to the armhole opening. These stitches will not be seen in the finished garment, as they are made slightly inside the seam.