Babies should sleep in a fitted one-piece sleeper or a wearable sleep sack, with no loose blankets, pillows, or extra bedding in their sleep space. The safest setup is a firm, flat mattress with only a fitted sheet, placed in a crib, bassinet, or portable play yard. What your baby wears on top of that depends on their age, the room temperature, and whether they’ve started rolling.
Sleepwear Options by Age
For newborns up to about 3 months, a swaddle is a popular choice. Swaddling mimics the snugness of the womb and helps quiet the startle reflex, that involuntary arm-flinging motion that wakes babies up. You can use a swaddle blanket wrapped snugly or a zip-up swaddle product designed to keep the wrap secure.
Once your baby shows signs of rolling, swaddling is no longer safe. Most babies hit this stage between 3 and 6 months. Signs to watch for include pushing up on their hands during tummy time, attempting to roll their body when unswaddled, or fighting the swaddle when you put it on. Even if your baby hasn’t rolled yet but the startle reflex has faded (typically around 4 to 6 months), it’s time to transition out of the swaddle.
After swaddling, the go-to option is a wearable sleep sack. These are essentially sleeping bags with arm holes. They keep your baby warm without any loose fabric that could cover their face. Sleep sacks work well from infancy through toddlerhood, and many parents use them until age 2 or beyond.
A simple footed pajama or onesie also works, especially in warmer months when an extra layer isn’t needed. The key rule: whatever your baby sleeps in should have no hood, no drawstrings, and fit snugly enough that it won’t ride up over their face.
How to Dress for Room Temperature
Sleep sacks are rated by TOG, a measurement of thermal resistance. A higher TOG means a warmer garment. Matching the right TOG to your nursery temperature prevents both overheating and chilling.
- Above 80°F (27°C): A 0.2 TOG sack or just a onesie. This is essentially a single thin layer.
- 73 to 79°F (23 to 26°C): A 0.5 TOG sack over a short-sleeve bodysuit.
- 68 to 73°F (21 to 23°C): A 1.0 TOG sack, which suits most climate-controlled homes year-round.
- 61 to 68°F (16 to 20°C): A 2.5 TOG sack over a long-sleeve onesie or footed pajama.
- Below 60°F (16°C): A 3.5 TOG sack with warm pajamas underneath.
A good rule of thumb: dress your baby in one layer more than you’d be comfortable wearing in the same room. If you’d sleep in a T-shirt, your baby likely needs a onesie plus a light sleep sack.
No Hats, No Blankets, No Extras
The sleep space should be completely bare except for a fitted sheet. That means no loose blankets, pillows, stuffed animals, crib bumpers, or sleep positioners. Young babies often cannot lift their heads to move away from soft objects that press against their face, creating a suffocation risk.
Hats are also off-limits for indoor sleep. Babies release a significant amount of body heat through their heads, and covering it can cause dangerous overheating. The only exceptions are the first hours after birth or in a neonatal intensive care unit, where temperature regulation needs are different.
Spotting Overheating
Overheating is a known risk factor for SIDS, so learning to check your baby’s temperature is worth the effort. The most reliable spot to feel is the back of the neck or the chest. Hands and feet tend to run cool in babies and aren’t a good indicator.
Signs your baby is too warm include flushed or red skin, sweating or damp hair, fussiness, and unusual sluggishness. Some babies overheat without sweating at all, so skin warmth and behavior are better clues than visible perspiration. If your baby feels hot to the touch, remove a layer and check again in 10 to 15 minutes.
Fabric Choices That Help
Cotton is the most common fabric for baby sleepwear. It’s breathable, natural, and widely available. The downside is that cotton absorbs moisture but doesn’t release it quickly, so a sweaty baby may stay damp.
Bamboo viscose has become a popular alternative. It wicks moisture away from the skin more effectively than cotton, keeping babies drier and cooler. It’s also exceptionally soft, which can be gentler on sensitive skin. For babies who run warm or sweat during sleep, bamboo-blend sleepwear is worth considering. Merino wool is another option for cold climates, as it naturally regulates temperature in both directions, but it’s pricier and harder to find.
Whatever the fabric, look for sleepwear that meets federal flammability standards. Snug-fitting pajamas and sleepwear labeled as such are designed to meet these requirements without chemical flame retardants.
Products to Avoid
Weighted sleep sacks, weighted swaddles, and weighted blankets are not safe for infants. The CPSC, AAP, CDC, and NIH have all issued warnings against these products. The added weight can restrict a baby’s chest movement and has been linked to lower oxygen levels during sleep, which may harm brain development. The AAP has specifically urged that weighted sleep products be removed from the market before they cause the kind of harm seen with inclined sleepers, which were associated with over 100 infant deaths before being recalled.
Other products to skip include sleep positioners (wedges or bolsters marketed to keep babies on their backs), inclined sleepers of any kind, and any product that hasn’t been specifically designed and tested as an infant sleep surface. If a product isn’t a standard crib, bassinet, or portable play yard, it’s not a safe primary sleep space, regardless of how it’s marketed.
The Sleep Surface Matters Too
What your baby sleeps on is just as important as what they wear. The mattress should be firm and flat. If you press your hand into it, it should spring back immediately rather than conforming to the shape of your hand. The fitted sheet should be taut, with no bunching or gaps at the edges where a small face could become trapped.
Place your baby on their back for every sleep, whether it’s a nap or nighttime. Once babies can roll both ways on their own, you don’t need to reposition them if they roll during sleep, but always start them on their back. Combined with a bare sleep surface and appropriate sleepwear, back sleeping is one of the most effective ways to reduce the risk of sleep-related infant deaths.