You can replace a worn-out slipper sole by making one from sturdy wool felt, which is sold by the yard at fabric stores. The felt sole could also give extra strength to knitted or crocheted slippers. The sturdiness of the wool felt eliminates need for any edge finishing of the sole, and the material can be stitched through with a standard needle and thread. Special paint found at craft stores will make the soles safely non-slip.
Stand on the craft paper and draw the outline of your foot with a pencil. Cut out the outline with the scissors for a sole template.
Pin the template to the wool felt and cut out the felt.
Flip the template to the opposite side, pin it to the felt for the other sole, and pin and cut out the sole.
Pin the soles to the bottoms of the slippers. Hand-stitch through the soles and the slippers with a straight stitch 1/4 inch from the edges of the felt, using the needle and carpet thread.
Draw slanted parallel lines on the bottom of the soles with the puffy paint. Let the paint dry for 24 hours.