Ribbing can be both functional and decorative. Ribs give your edges strength and elasticity because they usually have a denser stitch gauge than the main fabric; they keep the edges from flaring out and help the piece hold its shape by bouncing back after being stretched.
There are many types of ribs. All ribbing is based on repeated knit and purl combinations. The most popular ribs are k1, p1 rib or k2, p2 rib, as shown in Photos 9 and 10. These ribs (also referred to as 1x1 rib or 2x2 rib) are very elastic and easily bounce back to shape after being stretched. They make perfect neck edges.
Ribs do not have to have the same number of knit and purl stitches. Some pieces look best with k2, p1 ribs or k1, p3 ribs.
The combinations are endless!