Are sleep sacks safer than blankets?

What the evidence says

Canadian guidance is clear on this one: babies don't need loose blankets in their sleep space, and if you want to keep your baby warm, a properly fitted sleep sack is the safer choice. Loose blankets can shift and cover a baby's face or head during sleep, which raises the risk of overheating or suffocation.

If you do use a sleep sack, sizing matters a lot. One that's too big can let your baby slip down inside with their head covered, while one that's too tight can restrict hip and leg movement, which is especially risky if your baby rolls onto their tummy.

Health Canada and the Canadian Paediatric Society both note that if a blanket must be used for any reason, a thin, lightweight, breathable one is safer than a thick or heavy one. But sleep sacks remain the recommended default for most families. U.S. guidance from the AAP and CDC lines up with this, describing sleep sacks as a safe alternative to loose bedding.

One caveat: weighted sleep sacks or weighted blankets are not recommended by any of these organizations, regardless of size or fit, because of separate safety concerns.