Babies sleep safest and most comfortably in one layer more than what you’d wear in the same room. For most homes, that means a onesie or footed pajamas paired with a wearable sleep sack, with no loose blankets, hats, or heavy layers in the crib. The specifics change with your baby’s age, the room temperature, and the season, so here’s how to get it right.
The One-Layer Rule
Both the American Academy of Pediatrics and the UK’s National Health Service recommend the same simple guideline: dress your baby in one extra layer compared to what you’re comfortable wearing. If you’re fine in a t-shirt, your baby likely needs a short-sleeve onesie plus a light sleep sack. If you’d want a sweatshirt, bump up to a long-sleeve onesie under a warmer sack.
This rule works because babies lose heat quickly through their heads and extremities but can’t kick off blankets or unzip a too-warm outfit the way an adult would push covers aside. One extra layer compensates for their smaller body mass without trapping dangerous amounts of heat.
Room Temperature Sets the Starting Point
The Lullaby Trust recommends keeping your baby’s room between 61°F and 68°F (16 to 20°C). Many North American homes run warmer than that, closer to 68 to 72°F, which is still fine as long as you adjust what your baby wears. A simple thermometer in the nursery takes the guesswork out of it.
Here’s a practical breakdown by room temperature:
- 75°F to 81°F (warm summer nights): A short-sleeve onesie or even just a diaper under a very light 0.2 TOG sleep sack.
- 68°F to 75°F (typical indoor range): A onesie or footed pajamas with a 1.0 TOG sleep sack.
- 61°F to 68°F (cooler rooms): A long-sleeve onesie or pajamas under a 2.5 TOG sleep sack.
What TOG Ratings Mean
TOG stands for Thermal Overall Grade, and it measures how much warmth a fabric traps. The higher the number, the warmer the garment. Most sleep sacks list a TOG rating on the packaging, which makes matching the sack to your room temperature straightforward. A 0.2 TOG sack feels like a light cotton sheet. A 1.0 TOG is a comfortable middle weight. A 2.5 TOG is roughly equivalent to a light quilt.
You don’t need to memorize these numbers. Just check the room temperature, glance at the TOG chart on the sleep sack’s label, and pick the right pairing. If your baby is sweating or their chest feels hot to the touch, drop down a level. If their chest or tummy feels cool, add a layer underneath.
Best Fabrics for Baby Sleepwear
Cotton, especially organic cotton, is the go-to for infant sleepwear. It’s breathable, soft, hypoallergenic, and works across seasons. Bamboo viscose is another strong option. It’s naturally moisture-wicking and temperature-regulating, so it pulls sweat away from the skin and feels silky against sensitive areas. Either fabric keeps your baby from overheating in summer while still providing warmth in cooler months.
Avoid polyester-heavy fabrics for the layer closest to your baby’s skin. Synthetic materials trap heat and moisture, which raises the risk of overheating and skin irritation. If a polyester-blend sleep sack is your only option, put a cotton onesie underneath to create a breathable buffer.
Swaddling and When to Stop
Swaddling can help calm newborns by mimicking the snug feeling of the womb, though the AAP notes that it does not reduce the risk of SIDS. If you swaddle, keep these rules in mind: always place your baby on their back, make sure the swaddle isn’t tight around the hips, and never use a weighted swaddle blanket.
The moment your baby starts showing signs of rolling over, swaddling needs to stop. A swaddled baby who rolls onto their stomach can’t use their arms to push up or reposition, which creates a suffocation risk. Most babies begin attempting to roll between 2 and 6 months, though some show signs as early as 8 weeks. Watch for these cues during playtime: pushing up on hands during tummy time, lifting legs and flopping them to the side, or consistently breaking free from the swaddle wrap.
The transition is simple. Move to a sleep sack with arms free. Many “transitional” sacks leave arms out while still providing a cozy fit around the torso, which helps babies who are used to the snug sensation of a swaddle adjust without losing sleep.
No Loose Blankets Until Age One
The AAP advises against any loose blankets, pillows, stuffed animals, or soft bedding in the crib for babies under 12 months. These items can cover a baby’s face and obstruct breathing. Sleep sacks exist precisely to fill this gap: they provide warmth without the suffocation risk of a loose blanket.
After your child’s first birthday, introducing a small, lightweight blanket is generally considered safe. Until then, the sleep sack is your blanket substitute.
Items to Keep Out of the Crib
A few specific items deserve their own callout because they seem harmless but carry real risks:
- Hats and beanies: Once you’re home from the hospital, skip indoor hats. Babies release excess heat through their heads, and a hat interferes with that cooling mechanism.
- Weighted blankets or sleepers: The AAP specifically warns against any weighted sleep product on or near your baby.
- Pacifier clips attached to clothing: Never attach a pacifier to your baby’s clothes or hang it around their neck during sleep. The cord is a strangulation hazard.
- Socks on warm babies: If your baby’s feet feel warm to the touch, socks are unnecessary and can contribute to overheating. Footed pajamas or a sleep sack already cover the feet.
Signs Your Baby Is Too Hot
Overheating during sleep is linked to an increased risk of SIDS, so it’s worth learning the warning signs. Touch the back of your baby’s neck or their chest (not their hands or feet, which are often cooler). If the skin feels hot or clammy, they’re overdressed.
Other signs include flushed or red skin, damp hair, unusual fussiness, rapid breathing, and sluggishness or excessive sleepiness. Keep in mind that babies can overheat without visibly sweating, so skin temperature is a more reliable check than looking for sweat.
Dressing a Baby With a Fever
When your baby is sick, your instinct might be to bundle them up. Do the opposite. Overdressing traps heat and can push the fever higher, while underdressing to the point of shivering causes the body to generate more heat, which also works against you.
Stick to a single layer of lightweight cotton, like a onesie or thin pajamas, with a 0.5 TOG sleep sack if the room is between 68 and 72°F. In warmer rooms above 72°F, a 0.2 TOG sack or just a short-sleeve onesie may be enough. Above 77°F, a diaper and thin cotton onesie can suffice. Skip heavy swaddles, beanies, and extra layers entirely. Keep the room between 68 and 72°F if possible, and check your baby’s chest temperature frequently through the night.