Babies sleep safest and most comfortably in one more layer than you’d need to feel comfortable in the same room. That simple rule covers most situations, but the specifics depend on your nursery temperature, the type of sleepwear you choose, and your baby’s age. The goal is keeping your baby warm enough without any risk of overheating, which is a bigger concern than most parents realize.
Start With Room Temperature
The recommended nursery temperature for babies is 16 to 20°C (roughly 61 to 68°F). Everything else flows from this number. If your home runs warmer or cooler, you’ll adjust layers accordingly, but getting the room into this range first makes dressing your baby much simpler.
A basic room thermometer near the crib is the easiest way to take the guesswork out of it. Nursery temperatures shift throughout the night, especially in seasons where heating cycles on and off, so placing the thermometer away from windows and vents gives you the most accurate reading.
Clothing Combinations by Temperature
Here’s a practical breakdown of what to put on your baby at different room temperatures:
- Above 75°F (24°C): A short-sleeve onesie alone, or a onesie with a very lightweight sleep sack (0.5 tog). In genuinely hot rooms, a diaper with a single light layer is fine.
- 68 to 75°F (20 to 23°C): A long-sleeve onesie or footed pajamas with a lightweight sleep sack (around 1.0 tog).
- 61 to 68°F (16 to 20°C): A long-sleeve onesie under footed pajamas, or a onesie paired with a warmer sleep sack (2.5 tog).
- Below 61°F (16°C): A long-sleeve onesie layered under footed pajamas plus a heavy sleep sack (3.5 tog).
These are starting points. Every baby runs a little warmer or cooler, so check on your baby after 15 to 20 minutes to see how they’re doing and adjust from there.
What Tog Ratings Mean
Tog is a measure of how much warmth a fabric traps. The higher the tog, the warmer the garment. Most sleep sacks list their tog rating on the packaging, and it’s the most reliable way to match sleepwear to your nursery temperature. A 0.2 tog sleep sack is barely more than a sheet, while a 3.5 tog feels like a cozy winter blanket. Choosing the right tog means you don’t have to pile on extra layers or worry about loose blankets.
Why Sleep Sacks Beat Blankets
The American Academy of Pediatrics is clear on this: keep all loose bedding out of the crib. That includes blankets, quilts, comforters, and nonfitted sheets. Soft objects near an infant’s face are the most common cause of accidental suffocation during sleep.
Sleep sacks (also called wearable blankets) solve the warmth problem without any of that risk. They keep your baby at a consistent temperature and can’t ride up over the face. Dressing in layers underneath a sleep sack is the preferred approach for keeping babies warm safely.
No Hats Indoors
This surprises many parents, but babies should never wear hats while sleeping inside. A baby’s head accounts for over 25% of their body’s surface area and is a primary way they release excess heat. Covering the head drastically reduces the body’s ability to cool itself through the scalp and face, cutting off heat loss from convection, radiation, and evaporation all at once.
Research on infant thermal regulation shows that when the head is covered, face and scalp temperatures can rise above core body temperature. This impairs the cooling of brain structures that control vital functions. The risk is especially serious if the baby is already warmly dressed or has a fever. Hats are appropriate in the first hours after birth in the hospital, but once you’re home, skip them for sleep entirely.
Fabric Matters More Than You’d Think
Cotton is the standard recommendation for baby sleepwear because it’s breathable and lightweight. It works well across most temperatures and doesn’t trap excessive heat against the skin.
Bamboo viscose has gained popularity for good reason. Its fibers are naturally hollow, creating tiny air channels that wick moisture away from skin roughly four times faster than cotton. Bamboo also adapts to temperature: it releases heat when your baby is warm and retains it when the room cools down. For babies who tend to run hot or sweat during sleep, bamboo is worth considering.
Fleece is the one to be cautious about. It’s made from polyester and works by trapping air between fibers to create insulation. That sounds cozy, but it doesn’t let the body breathe. In a heated indoor environment, fleece can trap heat so effectively that it becomes dangerous. It also holds moisture against the skin rather than wicking it away. Save fleece for stroller outings in cold weather, not for the crib.
Swaddling and When to Stop
Newborns often sleep well swaddled, with their arms snug against their body. A thin cotton or muslin swaddle counts as a layer, so factor it into your temperature calculations. In a room at 68°F, a swaddled baby in a onesie is typically dressed appropriately without anything else.
You need to stop swaddling at the first sign of rolling. That includes any of these early cues: lifting the head during tummy time, reaching for toys while on their stomach, or any noticeable strengthening of the neck muscles. The AAP recommends stopping swaddle use by 8 weeks because a baby who rolls while swaddled cannot use their arms to reposition, which increases the risk of suffocation.
The transition from swaddle to sleep sack doesn’t need to be dramatic. Many parents switch to an arms-free sleep sack, which keeps the familiar feeling of gentle pressure around the torso while freeing the arms. Expect a few restless nights during the switch, but most babies adjust within a week.
How to Check if Your Baby Is Too Warm
The best way to check is by touching the back of your baby’s neck or their chest. These areas give you a more accurate read on core temperature than hands or feet, which tend to feel cool even when the baby is perfectly comfortable. Warm, dry skin on the chest or neck means things are right. If the skin feels hot, clammy, or damp, remove a layer.
Signs of overheating to watch for:
- Flushed or red skin, especially on the face and chest
- Sweating or damp hair, though some babies overheat without visible sweating
- Fussiness or restless sleep that doesn’t have another obvious cause
- Rapid breathing or a fast heart rate
- Heat rash, which looks like tiny red bumps in skin folds, around the neck, or on the bottom
- Unusual lethargy, where the baby seems overly tired or difficult to wake
If you notice several of these signs together, undress your baby to a single light layer, offer a feeding to help with hydration, and let them cool down gradually. Overheating is a known risk factor for sleep-related infant deaths, so erring on the side of slightly cool is always safer than slightly warm.
Putting It All Together
The simplest approach: set your nursery to 68°F, put your baby in a cotton onesie and a 1.0 tog sleep sack, and check their chest after 20 minutes. That combination works for the majority of homes and seasons. From there, you add or subtract based on what you feel on their skin. One layer more than what keeps you comfortable, breathable fabrics, no loose bedding, no hats. That’s genuinely all there is to it.