Petersham ribbon is a thick, flexible corded ribbon with a scalloped edge, used in millinery and tailoring for its ability to be steamed and shaped to follow curves. Unlike the similar but stiffer grosgrain ribbon which has a flat, sealed edge, the picot or scalloped edge of petersham ribbon allows it to hold a specific curve, making it ideal for hat brims, waistbands, and corsetry. It is typically made from fibers like cotton, rayon, or viscose.