A mustard seed pillow is nothing but a small-sized pillow made for newborn babies. It is filled with mustard seeds common name) and once sealed, it is kept under a head for support. Why we use Mustard Seed Pillow Mustard seed pillow is used mainly to provide support and shape of the head. It is used widely to provide a more acceptable round head shape. Since babies are born with all sorts of shapes, especially those born with the help of forceps, women resort to using different ways to give their babies the ideal round shape. This is done in order to give a more refined, �normal� look to the head. OYO BABY Rai pillow helps your baby in shaping the best round head.