Babies 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. The general rule is to dress your baby in one layer more than you’d wear comfortably in the same room. Getting this right keeps your baby at a safe temperature and reduces the risk of suffocation and sudden infant death.
The Sleep Surface Matters First
Before thinking about what goes on your baby, get the sleep space right. Your baby needs a firm, flat mattress (not inclined or angled) inside a safety-approved crib, bassinet, or play yard. Cover it with a single fitted sheet and nothing else. Blankets, pillows, bumper pads, and soft toys all need to stay out of the sleep area entirely. These items can bunch up against a baby’s face and block breathing, even when they look harmless.
This bare-crib approach applies for the entire first year. It can feel stark, but the mattress and your baby’s clothing are the only two things that should be in there.
Best Sleepwear by Age
Newborns to Around 2 Months
Swaddling works well for newborns. Wrapping your baby snugly with arms tucked in helps quiet the startle reflex, the involuntary arm-flinging that wakes them up. You can use a traditional swaddle blanket (tucked securely, with hips loose enough to move) or a zip-up swaddle product, which is easier to get right. Underneath, a simple onesie or footed pajama is usually enough depending on room temperature.
When Rolling Starts (Often 2 to 6 Months)
You need to stop swaddling as soon as your baby shows signs of rolling over. For some babies this happens as early as 8 weeks. Watch for these cues during awake time: pushing up on their hands during tummy time, lifting their legs and flopping them to one side, or consistently breaking free of the swaddle. A swaddled baby who rolls onto their stomach has no way to push themselves back or clear their airway.
Once you drop the swaddle, switch to a wearable sleep sack. These are essentially sleeping bags with armholes. Your baby’s arms stay free, but their body stays warm without any loose fabric that could cover their face. Sleep sacks come in different warmth levels and work well through the entire first year and beyond.
Older Babies (6 to 12 Months)
Sleep sacks remain the safest option through at least age one. Some parents are tempted to introduce a blanket once their baby seems more mobile, but loose blankets aren’t recommended until after the first birthday. A sleep sack paired with appropriate pajamas keeps your baby warm without the risk.
Choosing the Right Warmth Level
Sleep sacks and some swaddles are rated using a TOG system, which measures thermal resistance. The higher the TOG number, the warmer the garment. Here’s a practical guide based on your room temperature:
- 0.2 TOG: For warm rooms, 75°F to 81°F. Essentially a single layer of lightweight fabric.
- 1.0 TOG: For typical room temperatures, 68°F to 75°F. The most commonly purchased weight.
- 2.5 TOG: For cooler rooms, 61°F to 68°F. Good for winter in drafty homes.
- 3.5 TOG: For rooms below 61°F.
The recommended room temperature for infant sleep is 61°F to 68°F (16 to 20°C), which is cooler than many parents expect. A room thermometer near the crib takes the guesswork out. If your room runs warm, go lighter on the TOG. If it’s on the cooler end, layer a long-sleeved onesie or footed pajama underneath a higher-TOG sack rather than adding blankets.
How to Tell If Your Baby Is Too Hot
Overheating is a genuine safety concern during sleep, not just a comfort issue. Check the back of your baby’s neck or their chest. If the skin feels hot or clammy, they’re overdressed. Other signs include flushed or red skin, damp hair, unusual fussiness, or seeming unusually sluggish and tired. Babies can overheat without visibly sweating, so skin temperature is a more reliable check than looking for sweat.
Cool hands and feet, on the other hand, are normal for babies and don’t necessarily mean they need more layers. The neck and torso tell the real story.
Fabrics That Work Best
Cotton and bamboo are the two most popular choices for baby sleepwear, and both perform well. Organic cotton is breathable, soft, and holds up through repeated washing. Bamboo fabric is naturally moisture-wicking and does a slightly better job regulating temperature in both directions, keeping babies cool in warmth and cozy in cold. It’s a particularly popular choice for sleep sacks and footed sleepers.
Synthetic fabrics like polyester tend to trap heat and moisture against the skin. They’re fine for daytime outerwear but not ideal for sleep, especially if your baby runs warm.
Products to Avoid
Weighted sleep sacks and weighted swaddles have become popular in recent years, marketed as helping babies sleep longer. They are not safe. The U.S. Consumer Product Safety Commission warns clearly against using any weighted blanket, swaddle, or sleep sack for infants, and multiple infant deaths have been linked to these products. The CDC and NIH echo this warning.
The problem is physiological. A newborn’s rib cage isn’t rigid, and even modest pressure can make it harder for them to breathe and for their heart to beat properly. There’s also evidence that weighted products can lower oxygen levels, which may harm a developing baby’s brain. Dr. Rachel Moon, who co-chairs the American Academy of Pediatrics’ task force on sudden infant death, has described these risks directly. If you already own a weighted sleep product, the safest choice is to stop using it.
Other items to skip: loose blankets of any kind, sleep positioners, crib wedges, and any product that props a baby at an incline for sleep. Car seats, swings, and bouncers are not safe sleep surfaces either, even if your baby falls asleep in one during a car ride. Move them to a flat surface when you can.
Putting It All Together
A simple setup works best. For a room kept around 68°F, a baby in a short-sleeved onesie inside a 1.0 TOG sleep sack is a solid starting point. For cooler rooms, swap to a long-sleeved footed pajama and a 2.5 TOG sack. For warm summer nights, a diaper and a lightweight 0.2 TOG sack may be all they need. Check the back of their neck after 20 minutes to see how they’re doing, and adjust from there.
The one-extra-layer rule is your simplest guide. If you’d be comfortable in a t-shirt and light blanket, your baby needs roughly that same warmth plus one additional layer, which the sleep sack provides. No complicated math required.