Cosy slipper socks are soft and warm on the feet and easy to knit or crochet. However, they slip and slide on hardwood floors and the unprotected soles wear out quickly. Non-slip soles stitched to the bottom of the slipper socks make them safer and protect them from soil and wear.
Put on the slipper socks then trace around each foot with a pencil onto paper on the floor.
Cut out the traced footprints.
Cut out two sole pieces from the non-slip fabric or the rug matting, using the traced footprints for the patterns.
Pin each sole piece to the bottom of the corresponding slipper sock while the socks are still on your feet. Use safety pins and take care to avoid poking your feet.
Take off the socks. Trace the sole placement on the socks using a pencil, fabric pencil or washable marker. Unpin and remove the soles.
Apply the fabric glue to the wrong side of the non-slip sole pieces, leaving an unglued 1/2 inch margin all around the outside edge. Glue the soles to the slipper socks, aligning them to the markings on the bottom of the socks. Allow the glue to dry thoroughly.
Stitch the edges of the glued soles to the knitted slippers. If you use a sewing machine, set it for a zigzag stitch and feed the socks into the sewing machine foot so that the needle stitches the zigzag across the edge of the non-slip sole, alternating a "zig" into the non-slip fabric followed by a "zag" in the knitting.
To hand sew the sole in place, use an overcast stitch. Use the thimble to protect your finger as you push the needle through the knitting and up into the non-slip fabric from beneath. Continue stitching all the way around the edge of the sole, and then secure the end of the thread by stitching multiple tiny stitches in the knit fabric. Zigzag all the way around the sole, then backstitch to secure the end of the stitching before you cut the threads.
Avoid stitching into the glue: It will clog the needle and cause the thread to fray and break.