Newborns should sleep in a fitted one-piece sleeper or a wearable sleep sack, placed on a firm, flat mattress with nothing else in the crib. No blankets, no pillows, no stuffed animals, no bumper pads. That bare setup is the safest sleep environment for the first year of life, and the specifics of what your baby wears and sleeps on matter more than most parents expect.
The Sleep Surface
Your newborn needs a firm, flat mattress inside a safety-approved crib or bassinet, covered only by a tight-fitting sheet. “Tight-fitting” means the sheet wraps fully around and under the mattress with no loose fabric that could bunch up near your baby’s face. After washing, sheets can shrink slightly, so look for ones designed to stay snug after multiple hot-water washes.
Nothing else belongs on that mattress. Soft bedding, including blankets, pillows, bumper pads, and plush toys, creates suffocation and entrapment risks. The mattress should not be inclined or angled. Swings, bouncers, car seats, and loungers are not safe sleep surfaces, even if your baby falls asleep in them.
Sleepwear Options by Age
For the first few weeks, most parents choose between two options: a simple footed sleeper (sometimes called a “onesie pajama”) or a swaddle. Both work well when used correctly.
Swaddles wrap snugly around your baby’s torso and arms, mimicking the feeling of the womb. They can help calm the startle reflex that wakes newborns. The key safety detail is what happens at the hips: traditional swaddling that pins the legs straight and pressed together increases the risk of developmental hip problems. Safe swaddling keeps the wrap snug around the chest and arms but leaves the hips and knees free to bend and spread naturally. Many modern swaddle wraps and swaddle sacks are designed with a roomy pouch at the bottom for exactly this reason.
You need to stop swaddling as soon as your baby shows signs of rolling over, which typically happens around 2 to 4 months. Once a swaddled baby can roll onto their stomach, they can’t use their arms to push up or reposition, which creates a suffocation risk.
Sleep sacks (also called wearable blankets) are the go-to option after swaddling ends, and many parents use them from day one. They’re essentially a zippered bag with armholes that replaces a loose blanket. Because they move with your baby and can’t ride up over the face, they’re considered one of the safest sleepwear choices through the entire first year.
Choosing the Right Warmth Level
Sleep sacks and swaddles are rated by a number called TOG, which measures how much warmth the fabric provides. A higher TOG means a warmer garment. Matching the TOG to your nursery temperature prevents both overheating and getting too cold:
- 1.0 TOG: Best for room temperatures between 68°F and 75°F, which covers most climate-controlled homes.
- 2.5 TOG: Designed for cooler rooms between 61°F and 68°F.
If your nursery runs warm (above 75°F), look for a lightweight option around 0.2 TOG or dress your baby in just a thin onesie. The recommended nursery temperature range is roughly 61°F to 68°F (16°C to 20°C), which feels slightly cool to most adults. That’s intentional. Babies regulate heat less efficiently than adults, and a room that feels comfortable to you may be too warm for a sleeping newborn.
Fabric Choices That Help Regulate Temperature
Cotton is the most common fabric for baby sleepwear, and it breathes well enough for most situations. Its main limitation is moisture: cotton absorbs sweat and holds it against the skin rather than pulling it away, which can leave your baby feeling clammy in warmer conditions.
Bamboo viscose has become increasingly popular because it handles heat and moisture differently. Testing shows bamboo fabric is roughly 20% more breathable than equivalent-weight cotton and reduces skin surface temperature 2 to 3 degrees Celsius faster. The fibers have natural micro-gaps that create ventilation channels, and they wick sweat outward to the fabric surface where it evaporates instead of trapping it. Bamboo is also naturally hypoallergenic, which can matter for babies with sensitive skin.
Muslin is another strong option, especially for warmer climates. Its open weave dries fast and allows good airflow. For cooler nurseries, a thicker cotton or bamboo fleece in a higher-TOG sleep sack provides warmth without needing a separate blanket.
What Not to Put on a Sleeping Newborn
No hats indoors. Babies lose excess heat through their heads, and covering that escape route raises the risk of overheating. Hats are appropriate in the first hours after birth in the hospital and in the NICU, but not for regular sleep at home. A hat can also slip down over a sleeping baby’s face.
No weighted swaddles, weighted blankets, or weighted sleepers. These products are marketed as calming aids, but they pose safety risks for sleeping infants and are specifically recommended against.
No loose blankets of any kind. Even a thin muslin blanket can shift over your baby’s face during sleep. If you’re worried about warmth, add a layer underneath the sleep sack (a bodysuit or footed pajama) rather than putting anything loose in the crib.
How to Tell if Your Baby Is Too Warm
Overheating is a risk factor for SIDS, so knowing the signs matters. The most reliable check is touching the skin on your baby’s chest or the back of their neck. If it feels hot or sweaty, your baby is too warm. Don’t rely on hands and feet, which are often cool even when the rest of the body is comfortable.
Other signs of overheating include flushed or red skin, damp hair, and a fine rash of tiny red bumps in skin folds (especially around the neck). In more serious cases, you might notice rapid breathing, a weak pulse, or skin that feels clammy. If your baby is sweating during sleep, remove a layer or switch to a lower-TOG sleep sack.
A good rule of thumb: dress your baby in one more layer than you’d be comfortable in at the same temperature. If you’re fine in a t-shirt, your newborn likely needs a onesie plus a lightweight sleep sack. If you’d want a light sweater, consider a footed pajama under a 1.0 TOG sack.
Putting It All Together
The simplest safe setup is a firm crib mattress with a fitted sheet, and a baby dressed in a onesie or footed sleeper inside a sleep sack matched to your room temperature. For the first couple of months, a properly designed swaddle that allows hip movement is also a safe choice. Keep the crib empty, keep the room cool, skip the hat, and check your baby’s chest if you’re unsure about temperature. That combination covers the vast majority of what keeps newborn sleep safe.