The simplest rule for dressing a baby to sleep is one more layer than what you’d comfortably wear in the same room. For most homes kept between 68 and 72°F, that means a onesie underneath a lightweight sleep sack. Getting this right matters more than it might seem: both overheating and getting too cold disrupt your baby’s sleep, and overheating is a known risk factor for SIDS.
Why Temperature Matters So Much
Babies can’t regulate their body temperature the way adults can. Their thermoregulatory systems are still developing, and during sleep, thermal stress can impair their arousal responses, breathing drive, and heart rate regulation. Several well-established SIDS risk factors, including overwrapping, bedroom heating, and bed sharing, are connected to thermal stress. This risk is particularly pronounced for babies older than two months.
The goal isn’t to keep your baby as warm as possible. It’s to keep them in a comfortable, stable range where their body doesn’t have to work hard to stay regulated.
Setting the Right Room Temperature
Keep your baby’s room between 68 and 72°F for sleep. Some guidelines allow up to 78°F, but the cooler end of that range is easier to dress for safely. A fan on low helps circulate air and has independently been associated with lower SIDS risk. If you don’t have a thermostat nearby, a simple room thermometer near the crib gives you an accurate read.
Understanding TOG Ratings
TOG stands for Thermal Overall Grade, and it’s the standard measurement for how warm a sleep garment is. The lower the number, the lighter and cooler the fabric. When you’re shopping for sleep sacks or wearable blankets, the TOG rating tells you which room temperatures that product is designed for:
- 0.2 TOG: Best for warm rooms, 75 to 81°F. This is barely more than a single layer of fabric.
- 1.0 TOG: The sweet spot for most homes, 68 to 75°F. A standard year-round sleep sack.
- 1.5 TOG: Suitable for slightly cooler rooms, 64 to 72°F.
- 2.5 TOG: For cold rooms, 61 to 68°F. Think unheated bedrooms in winter.
- 3.5 TOG: Only needed below 61°F, which is colder than most indoor spaces.
Once you know your room temperature and your sleep sack’s TOG rating, you adjust the layers underneath. In a 70°F room with a 1.0 TOG sleep sack, a long-sleeved onesie is usually enough. In a cooler room with a 2.5 TOG sack, you might add a bodysuit under the pajamas. The clothing layers underneath should always be thin and snug, never bulky.
What to Dress Baby In by Season
In summer or warm rooms above 75°F, less is more. A diaper with a sleeveless onesie may be all your baby needs, or a single layer under a 0.2 TOG sleep sack. Stick with lightweight, breathable fabrics like cotton or bamboo. On especially hot nights, a baby can sleep in just a diaper and a thin muslin swaddle or sleep sack.
In winter or cool rooms, layering is key but should stay controlled. A long-sleeved bodysuit under footed pajamas, paired with a 1.0 or 1.5 TOG sleep sack, works for rooms in the upper 60s. If the room drops into the low 60s, move to a 2.5 TOG sack. Resist the urge to pile on extra blankets. Loose blankets in the crib are a suffocation risk, which is exactly why sleep sacks exist.
Choosing the Right Fabric
Cotton is the standard recommendation for infant sleepwear: breathable, soft, and widely available. It handles warm temperatures well and washes easily. Bamboo viscose is another strong option. It’s naturally temperature-regulating, keeping babies warmer in cool conditions and cooler in warm ones. Bamboo also wicks moisture away from the skin, which helps if your baby sweats at night. Merino wool has similar thermoregulating properties but is less common in infant sleepwear and typically more expensive.
Whatever fabric you choose, look for snug-fitting sleepwear or garments labeled as flame-resistant, which is a federal safety requirement for children’s pajamas in the U.S.
What Not to Put on a Sleeping Baby
The American Academy of Pediatrics specifically recommends against several items that might seem helpful:
- Hats indoors: Babies lose excess heat through their heads, and covering the head during sleep increases overheating risk. Hats are useful in the first hours after birth and in the NICU, but not for routine sleep at home.
- Weighted sleep products: Weighted swaddles, weighted blankets, and weighted sleepers should not be placed on or near a sleeping baby. The AAP considers these unsafe regardless of the product’s marketing.
- Loose blankets: No blankets in the crib until at least 12 months. Use a wearable blanket or sleep sack instead.
Swaddling and When to Stop
Swaddling works well for newborns. It mimics the snugness of the womb and dampens the startle reflex that wakes young babies. But swaddling has an expiration date, and the deadline is non-negotiable: you need to stop swaddling as soon as your baby shows any signs of rolling over. On average, this happens between two and six months.
Signs it’s time to transition include rolling during playtime, pushing up on hands during tummy time, lifting legs and flopping them to the side, regularly escaping the swaddle, or a noticeably reduced startle reflex. A swaddled baby who rolls onto their stomach may not be able to roll back, which can restrict breathing. Once you see these signs, switch to a sleep sack with arms free.
How to Check if Your Baby Is Comfortable
Hands and feet aren’t reliable indicators of your baby’s core temperature. It’s normal for a baby’s hands and feet to feel cool, and cold extremities alone don’t necessarily mean your baby needs more layers. Instead, touch the skin on your baby’s chest or abdomen. It should feel warm but not hot or sweaty. If the chest feels cool, add a layer. If it’s damp or hot, remove one.
Signs of overheating include flushed cheeks, damp hair, a sweaty chest or back, rapid breathing, and restless sleep. Signs of being too cold include a cool torso, mottled skin, and fussiness. Checking once at bedtime and once before you go to sleep yourself is usually enough to catch any issues, especially on nights when the temperature shifts.
A Quick Reference by Room Temperature
- Above 75°F: Diaper or short-sleeved onesie alone, or with a 0.2 TOG sleep sack.
- 70 to 75°F: Long-sleeved onesie with a 1.0 TOG sleep sack.
- 65 to 70°F: Long-sleeved bodysuit and footed pajamas with a 1.0 to 1.5 TOG sleep sack.
- 60 to 65°F: Bodysuit under pajamas with a 2.5 TOG sleep sack.
- Below 60°F: Additional base layer under pajamas with a 3.5 TOG sleep sack. Consider warming the room.
These are starting points. Every baby runs a little warmer or cooler, and you’ll learn your baby’s tendencies quickly. The chest check is always the final word on whether you’ve got the layers right.