Swaddling has been around for ages as it helps to prevent the startle reflex. But forcing the baby's arms to their sides or over their chest prevents two natural behaviors that frustrate the baby and they fight to get their hands free. First - Over 90% of babies sleep with their ARMS UP around their head when placed on their back to sleep. This is simply a baby's natural and preferred way to sleep, just like in the womb! Second - All babies are born with the need to SELF-SOOTHE by touching their face and sucking on their hands as they did in the womb. This medically proven behavior is how a baby calms and falls back asleep on their own. Traditional swaddling prevents this. The patented wings on the Swaddle UP allow the baby to both sleep with their arms in their preferred ARMS UP position and gives enough movement so they can SELF-SOOTHE, all while calming down the startle reflex. The snug fit from our 4-way White stretch fabric of 93% Cotton and 7% Elastane creates a familiar and secure feeling just like in the womb to calm the Moro (startle) reflex. Does not contain flame retardants or any harmful chemicals. This extra warm 3.5 TOG Swaddle UP is ideal for temperatures 60°F & under. The multi-award winning zip-up swaddle that allows your baby to sleep in a more natural ARMS UP position.