Place the wool sweater in the lingerie bag and put it in the washing machine. Wash the sweater with hot water and 1/4-cup laundry soap. Dry the sweater on a flat surface for 24 hours. Cut apart the sweater at the seams.
Stand with bare feet on the craft paper and outline your feet with a pencil. Cut out the outlines 1-inch past the pencil line to create templates.
Pin the templates to the felted fabric. Cut out the fabric, making a right and left slipper sole.
Cut the templates in half, lengthwise. Pin the top halves of the templates to the felted fabric and cut out the fabric for the slipper tops.
Pin the slipper tops to the slipper bottoms, right sides of the fabric facing each other. Sew a straight stitch 1/4-inch from the edges with the sewing machine. Turn the slippers to the right sides.