Ribbing is a stretchy fabric created by alternating knit and purl stitches such that like stitches form vertical lines as the fabric is knit. Ribbing is used at the tops of socks and at the hems of sweaters and hats to keep edges neat and snug. Common ribbing patterns are knit 1, purl 1 and knit 2, purl 2, although some patterns use uneven numbers such as knit 3, purl 1 to create wide and narrow patterns.