How many layers should baby wear to sleep?

What does the evidence say about dressing a baby for sleep during pregnancy?

1. The room temperature for a sleeping baby should not be too hot; it should be comfortable for a lightly clothed adult, and a baby should not feel hot to the touch. There is no separate baby-specific thermostat number to hit beyond that adult comfort check. 1
2. A baby can become hot or overheated from wearing too many layers of clothes and bedding for the room's temperature, a pattern sometimes called overbundling. The practical rule is to dress the baby in clothes suitable for the actual temperature of the room they're sleeping in, not a fixed outfit used everywhere in the house. 2
3. Wearing a hat while indoors can make a baby too hot, so hats should come off once inside. For warmth, the guidance points to a wearable blanket or an extra layer of clothing rather than adding loose items to the sleep space itself. 2
4. Signs that a baby is too hot include sweating, flushed or hot-looking skin, and a chest that feels hot to the touch, which are the practical checks to use instead of guessing from room temperature alone. 2
5. CDC guidance separately reinforces not covering a baby's head and not letting a baby get too hot, naming sweating or a hot-feeling chest as the signs to watch for, which lines up with NIH's overheating checks. 3
6. For a baby who seems like they might get cold overnight, CDC points to sleep clothing and a wearable blanket, also called a sleep sack, as the safe option, rather than a loose blanket placed over or around the baby. 4
7. A crib holding nothing but a fitted sheet over the mattress may look bare, but NIH describes that as the safest setup, since quilts, blankets, sheepskins, and other soft coverings raise the risk of sleep-related infant death from suffocation and strangulation. Warmth is meant to come from the baby's own clothing and sleep sack, not from bedding added to the crib. 5

Checking if your baby's sleep setup is too warm