A sleeve head is used to fill out the ease area of a sleeve cap or “head.” In this method, you sew in the sleeve head BEFORE setting in the sleeve.
Purchase 1/4 yd. (25cm) of Armo-Rite or take apart an old tie! You can also use linen or loosely woven wool. Cut one bias strip 10-12" (30cm) long and 11/2" (4cm) wide for each sleeve.
Place the strip on the wrong side of the sleeve cap at the ease point notch. Lower the needle in the 5/8" (1.5cm) stitching line. Using a 4mm stitch length, start sewing.
Begin to pull on the bias strip firmly while stitching. It will get narrower as you stretch it so that it will be about 1/4” (6mm) from the edge of the cap. That is fine as you want a smaller amount in the seam allowance and a longer amount hanging down into the sleeve.
As you sew, make sure the edge of the cap stays next to your 5/8” marking on the machine.
The sleeve cap is automatically eased and ready to sew into the armhole.
If it seems awkward the first time, simply unstitch and redo. With a bit of practice, it will be easy.
Excerpted from Jackets for Real People