Rated America’s best baby swaddle, the SNOO Sleep Sack was designed by top pediatrician and world’s leading hip-safe swaddling expert, Dr. Harvey Karp. Perfect for healthy, growing hips. Made from luxuriously soft organic cotton with special wings that attach to the SNOO Smart Sleeper to keep babies safely on the back. Includes extra-quiet Velcro for escape-proof security and 2-way zipper that opens from top or bottom for easy midnight nappy changes.