How to Dress a Baby for Sleep: Layers, Sleep Sacks, and Not Overheating

It is 10 p.m., the thermostat says one thing, the window feels like it says another, and you are standing over a drawer trying to decide between the fleece sleeper and the cotton one. Underneath the question is a quieter one: what if I get this wrong and my baby is too cold all night?

Here is the reassuring part. The official guidance on how to dress a baby for sleep is short, it is the same across the two biggest sources in the United States, and it does not involve a thermometer or a chart. It is one sentence long. Here it is, along with what goes on top of it, what stays out of the crib entirely, and how to tell in three seconds whether you got it right.

01The one-layer rule

The whole thing rests on a single instruction, and both major sources word it almost identically. The American Academy of Pediatrics puts it this way: "In general, you should dress your baby in only one layer more than you're wearing." The NIH's Safe to Sleep campaign, run by the National Institute of Child Health and Human Development, says the same thing from the other direction: "Don't let baby get too hot during sleep. Dress your baby in no more than one layer more of clothing than an adult would wear to be comfortable."

Read that carefully, because the wording is doing real work. It is one layer more than you are wearing in that same room, right now — not one layer more than an average person on an average night. If you are comfortable in a t-shirt, your baby is in a bodysuit plus one thing. If you are under a heavy comforter in a cold room, that changes the math, and it is worth noticing that you are the one with the comforter and your baby cannot have one.

The AAP's general newborn dressing guide repeats the same rule word for word — "dress the baby in one more layer of clothing than you are wearing to be comfortable in the same environment" — and adds one exception worth knowing: a premature baby "may need still another layer of clothing until his or her weight reaches that of a full-term baby," because a smaller body has a harder time holding its own temperature. If your baby came early, ask your pediatrician what that means for your house specifically.

02What that looks like in real clothes

"One layer" is a principle, not an outfit. In practice, a sleep layer is usually one of two things, and the NIH names both: "A one-piece sleeper or wearable blanket can be used." So the working combinations most parents land on look like this.

• A warm room, and you're in a t-shirt. A short-sleeve cotton bodysuit, or a lightweight one-piece sleeper on its own.
• A normal room, and you're in pajamas. A bodysuit or footed sleeper, plus a wearable blanket over it.
• A cool room, and you'd want a sweatshirt. A long-sleeve footed sleeper in a heavier fabric, plus a wearable blanket — rather than more blankets in the crib, which is not an option.
• A hot room. Fewer layers, not more, and the AAP's dressing guide is explicit that above about 75°F you can reduce your baby "to a single layer."

One clarification, because the AAP's general dressing page can be confusing if you read it next to the sleep guidance. That page mentions wrapping a baby in a receiving blanket in cooler weather — but that is about a baby in your arms, not a baby in a crib. Once your baby is in their sleep space, loose blankets are out. That is what wearable blankets exist to replace.

03Why a wearable blanket, not a blanket

A wearable blanket — often sold as a sleep sack — is a sleeveless bag your baby wears, so the warmth cannot slide up over their face. That is the entire reason it is recommended. The AAP's guidance is to "dress them in layers of clothing or use a wearable blanket," and the NIH says to "dress baby in a wearable blanket or an extra layer of clothing to keep them warm without adding items to the sleep area."

The other half of that sentence is the important one. The AAP asks parents to "keep soft objects & loose bedding out of your baby's sleep area," and the list is longer than most people expect: "pillows and pillow-like toys, quilts, comforters, mattress toppers, non-fitted sheets, blankets, toys, bumper pads or related products that attach to crib slats or sides." A fitted sheet on a firm mattress, and your baby — that is the whole sleep space. The AAP's test for firm is refreshingly concrete: "a firm surface means that it shouldn't indent when your baby is lying on it."

04Too hot is the risk, not too cold

Most of us instinctively worry about a cold baby. The guidance worries about a hot one, and it says why plainly. The NIH's risk-reduction page describes the problem — "baby can get hot or overheated if they are wearing too many layers of clothes and bedding for the room temperature (sometimes called overbundling)" — and then names the stakes: "overheated babies are at higher risk for SIDS and heat-related death."

That risk is the whole reason safe sleep guidance exists. The CDC reports that "in 2024, about 3,400 babies died suddenly and unexpectedly in the United States," and says it "supports the 2022 recommendations issued by the American Academy of Pediatrics to reduce sleep-related infant deaths." Overheating is one of the few pieces of that picture a parent can control with a decision as small as which sleeper to grab.

It also means the safe direction to err is cool. An extra layer has a real downside; one fewer layer, in a room you find comfortable, mostly does not.

05How to check: the chest, not the hands

Both sources point you to the same place, and it is not where most people reach first. The AAP says to "check your baby for signs of overheating such as sweating, a hot chest or flushed skin." The NIH lists the same three: "watch for signs that baby is too hot, such as sweating, flushing/red or hot skin, or baby's chest feeling hot to the touch."

Doing this once during a night feed is enough. You do not need to keep checking, and you do not need a monitor that grades you on it.

06What about a room thermometer?

You will see a specific number — usually 68 to 72°F — repeated almost everywhere online as the correct nursery temperature. We are not going to state it as guidance, because we could not find it in the AAP or NIH material we read for this piece. What those sources say instead is looser and, honestly, more usable: the NIH's instruction is to "dress baby in clothes suitable for the temperature of the room," and the AAP anchors everything to what you find comfortable in that room.

So a thermometer is optional. Your own comfort is the instrument the official guidance actually asks you to use, and unlike a number on a wall it accounts for humidity, drafts, and the fact that the nursery is often the coldest or hottest room in the house. If you want a number, ask your pediatrician what they recommend for your baby — that answer will be better than an internet average.

07If you're swaddling, the layer math changes

A swaddle is a layer. That sounds obvious, and it is the single easiest way to accidentally overdress a newborn — a fleece sleeper plus a thick swaddle is two warm layers, not one. The AAP's swaddling guidance says it directly: "swaddling can increase the chance your baby will overheat, so avoid letting your baby get too hot." Dress lighter underneath a swaddle than you would under a sleep sack.

The rest of the AAP's swaddling rules are worth having in one place while you are thinking about what your baby wears at night:

• Leave room at the chest. "You want to be able to get at least two or three fingers between the baby's chest and the swaddle."
• Leave the hips loose. "Make sure their hips can move and that the blanket is not too tight" — because "straightening and tightly wrapping a baby's legs can lead to hip dislocation or hip dysplasia."
• Back only. "If babies are swaddled, they should be placed only on their back and monitored so they don't roll over."
• Stop at the first sign of rolling. "Stop swaddling as soon as your baby shows any signs of trying to roll over" — and the AAP repeats it in the sleep guidance: "when your baby looks like they're trying to roll over, you should stop swaddling them."

That last one is why most families move from a swaddle to a wearable blanket somewhere in the second or third month. It is the same job — warmth without anything loose — in a form that keeps working once your baby starts rolling. Our step-by-step guide to swaddling covers the wrap itself, and our safe sleep guide covers everything around it.

08The short version, at 2 a.m.

Dress your baby in one layer more than you are wearing in that room. Make the extra layer a wearable blanket rather than a loose one. No hat, nothing weighted, nothing else in the crib. Touch their chest once during a night feed, and if it is sweaty or hot, take something off.

That is the whole method, and it does not get harder as your baby grows. The rest of the newborn learning curve — feeding, burping, diapers, and when to call the doctor — is on our newborn basics guide, sourced the same way this page is. And if you are still pregnant, our free week-by-week planner puts the sleep setup where it belongs: done early, so the 2 a.m. version of you is only making one decision instead of five.

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Newborn Weeks is planning help, not medical advice — always follow your own doctor, midwife, or pediatrician.