The safest option for baby sleep is a fitted onesie or footed pajamas paired with a wearable blanket (sleep sack), with no loose blankets, pillows, or hats in the crib. The exact combination depends on your baby’s age and the temperature of the room, but the core rule is simple: one layer of snug clothing plus a sleep sack replaces everything a blanket would do.
Safe Sleepwear Basics
The American Academy of Pediatrics is clear: keep loose blankets, pillows, stuffed toys, bumpers, and all other soft items out of the sleep space. That means no tucking a traditional blanket around your baby, no matter how thin it is. Instead, wearable blankets and sleep sacks serve as the blanket replacement, keeping your baby warm while eliminating suffocation risk.
Your baby should also sleep with their head uncovered. No hats or beanies indoors during sleep. Babies release excess heat through their heads and faces, and covering them creates a real risk of overheating. Research from neonatal intensive care units found that hats were unnecessary for maintaining body temperature once infants were in an open crib, and removing them reduced the risk of both overheating and suffocation. This applies at home too.
Sleepwear by Age
Newborns (0 to 2 Months)
Swaddling works well for newborns. A lightweight swaddle blanket wrapped snugly around your baby’s body helps calm the startle reflex, which is the involuntary arm-flinging motion that jolts babies awake. You can also use a zip-up swaddle product, which is easier to get right than a traditional blanket wrap. Underneath the swaddle, a short-sleeve or long-sleeve onesie is typically enough depending on room temperature.
The critical rule with swaddling: stop as soon as your baby shows any signs of trying to roll over. Some babies start working on rolling as early as 2 months, though it varies. Once you see the first hints of rolling, the swaddle needs to go, because a swaddled baby who flips onto their stomach cannot push themselves back over.
After the Swaddle (2 to 12 Months and Beyond)
Once your baby outgrows the swaddle, a sleep sack is the go-to. Sleep sacks are wearable blankets that zip up and have openings for the arms, keeping your baby’s arms free while covering their torso and legs. They can be used from birth, but they’re especially useful during the transition out of swaddling because they still provide that cozy, enclosed feeling without restricting arm movement.
There’s no set age when babies need to stop using a sleep sack. Many are sized for toddlers and even older children. As long as the fit is appropriate and not too large, a sleep sack remains a safe alternative to blankets for as long as your child will wear one.
Dressing for Room Temperature
A good rule of thumb: dress your baby in one more layer than you’d find comfortable in the same room. But the more precise approach uses TOG ratings, which measure the thermal resistance of a sleep sack. Higher TOG means warmer.
- 75°F to 81°F (warm room): A short-sleeve onesie or just a diaper, paired with a 0.2 TOG sleep sack (essentially a thin muslin layer).
- 68°F to 75°F (comfortable room): A long-sleeve onesie or footed pajamas with a 1.0 TOG sleep sack. This is the sweet spot for most nurseries.
- 61°F to 68°F (cool room): A long-sleeve onesie with a 2.5 TOG sleep sack, which provides significant warmth.
For the most common nursery temperature of around 68 to 72°F, a long-sleeve cotton bodysuit under a 1.0 to 1.5 TOG sleep sack works well for most babies. If your baby tends to run warm, drop to a short-sleeve layer underneath. If they run cool, go with footed pajamas under the sack.
How to Check if Your Baby Is Too Hot
Feel the skin on your baby’s chest or back. It should feel warm but not hot or sweaty. Don’t rely on hands or feet, which are often cooler than the rest of the body and can be misleading. If your baby’s chest feels damp or flushed, remove a layer.
Overheating during sleep has been linked to sudden unexpected death in infancy, including SIDS. This is one of the reasons loose blankets are discouraged. Parents tend to pile on blankets when they worry about cold, but slight coolness is far safer than overheating. If you’re unsure, err on the lighter side.
Choosing the Right Fabric
Cotton is the most reliable all-around choice for infant sleepwear. It’s breathable, holds its shape after repeated washing, and provides steady temperature regulation. Organic cotton performs the same way and avoids potential chemical residues from conventional processing.
Bamboo fabric is softer to the touch and often marketed as more breathable, but many parents find it runs cooler than cotton and can feel clingy when damp. That makes bamboo a reasonable choice in warm climates or for babies who overheat, but less ideal if your nursery runs cool. Fleece is warm but traps heat, so it’s best reserved for very cold rooms and paired with a lower-TOG sleep sack or used as the sleep sack fabric itself rather than layered underneath one.
Practical Features That Matter at Night
You’ll be doing diaper changes in the dark or near-dark, possibly multiple times a night. A two-way zipper, which opens from the bottom up, lets you access the diaper without unzipping the whole garment and exposing your baby’s chest to cool air. This single feature can mean the difference between a baby who stays drowsy during a change and one who wakes up fully.
Footed pajamas are convenient because they eliminate the need for socks, which babies kick off constantly. For newborns, gowns with an open bottom provide the fastest diaper access of any style, though they’re less useful once babies start moving around. Snap closures work fine but are slower and more fumble-prone at 3 a.m. than zippers.
What Not to Put Baby to Sleep In
Weighted sleep sacks and weighted swaddles have become popular, but the AAP has not endorsed them. The concern is that added weight on a baby’s chest could restrict breathing or make it harder to roll to a safe position. Standard, unweighted sleep sacks are the recommended option.
Avoid any sleepwear with hoods, drawstrings, or ties, which pose strangulation or suffocation risks. Loose socks or mittens can come off and become a choking hazard in the crib. If your baby scratches their face, look for onesies with fold-over hand cuffs built into the sleeves rather than adding separate mittens.
Babies should also not sleep in outdoor clothing like snowsuits or bunting bags once you’re indoors. These are designed to trap heat and will quickly cause overheating in a temperature-controlled room. Remove the outer layer when you get home, even if your baby fell asleep in the car seat on the way.