Sleep sack

A sleep sack is a wearable blanket, essentially a soft fabric bag with armholes, that zips or snaps closed around the baby's body. It keeps the baby warm through the night without a loose blanket that could shift over the face. Sleep sacks are typically introduced once swaddling ends, and many families use them well into the toddler years.

Sizing is based on the baby's height and weight rather than age alone, and most brands publish a size chart since babies grow at different rates. The other variable is warmth, which is expressed as a TOG rating, so pairing the right size with the right TOG for your room temperature matters more than picking a specific brand. Some sleep sacks include hip-healthy room for leg movement, which is worth checking for the newborn stage.

A frequent mistake is sizing up too far for a baby to grow into, which can let the sack sit loosely around the neck or arms. Another is layering a sleep sack over regular clothing without adjusting for the added warmth, leading to overheating. Once a baby can climb or is pulling to stand, check that the sack does not restrict leg movement enough to cause a trip.