My Strollers.com

Flat Head Syndrome" is a condition where the back of a baby's head becomes flattened due to the pressure of sleeping on the back, which is the recommended sleeping position for babies. Nestle your little one in the Boppy Noggy Nest head support pillow which raises your baby's head so that it isn't laying flat against a hard surface, thus preventing "Flat Head Syndrome." A patented design includes a cut-out hole to relieve pressure from the back of your baby's head, helping to maintain the roundness of his or her head. Generous side padding provides comfort while luxurious fabric comforts your baby all over.
BabyEarth.com

The Noggin Nest Head Support, with a unique patented cut-out design, is the only head support to help guard against "Flat Head Syndrome." This necessary cushion works by slightly raising baby's head so that it isn't lying flat against a hard surface. Use the Boppy Noggin Nest head support in baby’s bouncer, swing or stroller.