Sleep sacks (aka wearable blankets) safely provide an extra layer of warmth without restricting a baby's arms. When used as part of a consistent sleep routine, sleep sacks can also help cue that it's time to transition to sleep, which can translate into an easier bedtime. 

The standard sleep sack forms a pouch around the baby's legs, which allows for plenty of freedom of movement (but makes it harder for a toddler to throw a leg over the side of the crib and climb out). Will a sleep sack magically turn your baby into a champion sleeper all on its own? Probably not. However, it can safely provide warmth and comfort to your child.

If you're wondering why you can't just use a blanket to keep your baby warm, here's the answer: the American Academy of Pediatrics (AAP) recommends keeping loose blankets and unfitted sheets out of a baby's sleep space for the first 12 months of life to reduce the risk of sleep-related injury. Sleep sacks are a safer alternative.