Babies should sleep on a firm, flat mattress in a safety-approved crib, wearing a fitted sleep sack or simple sleepwear with no loose blankets, pillows, or soft items in the sleep area. Getting this right involves choosing the right surface, the right clothing layers, and the right room conditions, all of which change as your baby grows.
The Sleep Surface
The safest place for a baby to sleep is a firm, flat mattress inside a safety-approved crib, bassinet, or play yard, covered only by a fitted sheet. “Firm” means the mattress should not conform to your baby’s face or head when they press against it. Crib mattresses sold in the United States must pass a federally mandated firmness test set by the Consumer Product Safety Commission, so buying a new, compliant mattress takes much of the guesswork out of it. Used or hand-me-down mattresses can be riskier because they may have softened over time or lost structural integrity.
Inclined sleepers, swings, bouncers, car seats, and adult beds are not safe sleep surfaces. Inclined products like the Rock ‘N Play were linked to over 100 infant deaths before being pulled from the market. Even if your baby falls asleep in a car seat during a drive, move them to a flat surface as soon as you can.
What to Keep Out of the Crib
The crib should contain nothing except your baby and the fitted sheet. That means no blankets, pillows, bumper pads, stuffed animals, or positioning devices. Every one of these items increases the risk of suffocation. It can feel counterintuitive to put a baby down in what looks like a bare, uncomfortable space, but infants do not need the cushioning adults rely on, and the flat, clear surface is what protects them.
Sleepwear: Sleep Sacks and Swaddles
Since loose blankets are off-limits, a wearable blanket (sleep sack) is the go-to way to keep your baby warm at night. Sleep sacks zip around the torso and leave nothing that can ride up over the face. For newborns, a swaddle wrap serves a similar purpose while also calming the startle reflex that can jolt babies awake.
Swaddling has a firm expiration date. You need to stop swaddling once your baby shows any signs of trying to roll over, which can begin as early as 2 months. A baby who rolls onto their stomach while swaddled may not be able to roll back, creating a suffocation risk. Most babies begin rolling between 3 and 6 months, and the startle reflex that makes swaddling helpful typically fades around 4 to 5 months. A transitional sleep sack with arms free is a good bridge between swaddling and a standard sleep sack.
Weighted Sleep Sacks
Weighted swaddles and sleep sacks are marketed as helping babies sleep longer, but they are not safe. The AAP has called weighted sleep products “not safe for infants,” warning that the added pressure on a newborn’s still-flexible rib cage can restrict breathing and affect heart function. There is also evidence that weighted products can lower oxygen levels, which may harm a developing brain. The Consumer Product Safety Commission has urged retailers to stop selling them. Skip these entirely.
Choosing the Right Warmth: TOG Ratings
Sleep sacks are rated by a unit called TOG, which measures thermal resistance. The higher the TOG number, the warmer the garment. Matching the TOG to your room temperature prevents both overheating and chilling:
- 0.2 TOG: Best for warm rooms, 75°F to 81°F
- 1.0 TOG: Best for 68°F to 75°F, the most common indoor range
- 1.5 TOG: Best for 64°F to 72°F
- 2.5 TOG: Best for cooler rooms, 61°F to 68°F
- 3.5 TOG: Best for rooms below 61°F
Underneath the sleep sack, what your baby wears depends on the room temperature and the TOG of the sack. In a 70°F room with a 1.0 TOG sack, a long-sleeved onesie is usually enough. In a warmer room with a lighter sack, a short-sleeved bodysuit or even just a diaper may be all that’s needed. In a cooler room with a higher-TOG sack, adding a layer like footed pajamas under the sack makes sense. The goal is always to dress your baby in one layer more than you’d comfortably wear yourself in the same room.
Fabrics That Work Best
Cotton is the most common and affordable choice for baby sleepwear. It’s soft, breathable, and widely available, especially in organic varieties. Its main drawback is that it absorbs moisture and holds it against the skin rather than wicking it away, which can feel clammy in humid conditions or if your baby sweats at night.
Bamboo viscose has become a popular alternative. It’s roughly 20% more breathable than cotton, naturally wicks moisture, and keeps skin about 2 to 3 degrees Celsius cooler under identical conditions. The fibers are smooth and round, making them a good fit for babies with eczema or sensitive skin. Bamboo costs more per garment, but many parents find the temperature regulation worth it, especially in warmer climates. Either fabric works well. The more important factor is getting the right TOG and layering for your room temperature.
Room Temperature and Overheating
The ideal room temperature for infant sleep falls between 68°F and 72°F (20°C to 22°C). Anything above 72°F may be too warm. This matters because overheating is an independent risk factor for SIDS, and babies are particularly vulnerable because they can’t regulate their own body temperature well yet. They also sweat less than adults, meaning they have fewer built-in ways to cool down.
Check your baby’s temperature by feeling their chest or the back of their neck, not their hands or feet, which tend to run cooler naturally. Signs of overheating include skin that feels hot to the touch, flushed or red skin, damp hair, fussiness, or unusual sluggishness. A baby can be overheating even without visible sweating. If your baby feels warm, remove a layer or lower the room temperature rather than waiting to see if they cool down on their own.
Hats and beanies should not be worn during indoor sleep. Babies release excess heat through their heads, and covering it interferes with that cooling mechanism. Save hats for outdoor time in cold weather.
What Changes as Your Baby Grows
Newborns (0 to 2 months) do well in swaddle wraps or swaddle-style sleep sacks that keep arms snug. Once rolling signs appear, transition to a sleep sack with arms free. Most babies use sleep sacks comfortably through their first year and often well into toddlerhood. Once your child is old enough to climb out of the crib (usually around 18 to 24 months, though it varies), many families transition to a toddler bed, and at that point a small, lightweight blanket becomes an option.
Throughout every stage, the core rules stay the same: firm and flat surface, nothing loose in the sleep space, and clothing layers matched to the room temperature. If you remember nothing else, remember that bare is better. A baby in a properly chosen sleep sack on a bare crib mattress is safer than a baby surrounded by cozy-looking blankets and bumpers.