The HALO SleepSack Swaddle replaces loose blankets in the crib that can cover your baby's face and interfere with breathing. In addition to helping your baby sleep safer, it helps him sleep better, too. Its adjustable swaddle wrap immobilizes your baby's arms to prevent the "Moro" or startle reflex. And, it is the only 2-in-1 adjustable swaddle that allows for swaddling arms in or arms out for baby's comfort and to ensure an easy and gentle transition to the SleepSack Wearable Blanket when it is time to stop swaddling. Used in hospital nurseries nationwide, the HALO SleepSack Swaddle is the #1 choice of hospital nurseries, recommended by safety organizations and is recognized as "Hip Healthy" by the International Hip Dysplasia Institute. Use over regular sleepwear to take the place of loose blankets. Discontinue swaddling when the baby shows signs of rolling over or breaking out of the swaddle wrap. 100% polyester micro fleece. Size small fits 13-18 lbs.