Dress your baby in no more than one layer beyond what you’d wear comfortably in the same room. That single rule, recommended by the American Academy of Pediatrics, covers most situations. In practice, it means a onesie plus a wearable sleep sack in a room kept between 68 and 72°F, adjusting up or down based on the temperature your baby actually sleeps in.
The One-Layer Rule
If you’d sleep comfortably in a t-shirt and light blanket, your baby needs roughly the same warmth, plus one extra layer. Babies lose heat faster than adults because of their higher surface-area-to-body-weight ratio, but they also can’t kick off a blanket or tell you they’re too warm. That’s why the guidance exists: it keeps you from underdressing and overdressing at the same time.
In most homes, this translates to a short- or long-sleeve bodysuit underneath a sleep sack. Loose blankets, quilts, and pillows don’t belong in the crib. A wearable sleep sack replaces the blanket entirely, keeping your baby warm without the risk of fabric covering their face or getting tangled around their body.
Room Temperature and What to Pair With It
The ideal nursery temperature falls between 68 and 72°F for most babies, though anything in the 68 to 78°F range is considered acceptable. A simple thermometer in the room takes the guesswork out. Once you know the temperature, match clothing layers to it:
- 75°F and above: A diaper with a light 0.5 TOG sleep sack, or just a short-sleeve onesie. Some babies sleep fine in a diaper alone when rooms run hot.
- 68 to 73°F: A short-sleeve bodysuit with a 1.0 TOG sleep sack. This is the sweet spot for most nurseries.
- 61 to 68°F: A long-sleeve bodysuit and footed pants underneath a 2.5 TOG sleep sack.
- Below 61°F: Full footed pajamas with a 2.5 to 3.5 TOG sleep sack.
What TOG Means and Why It Matters
TOG is a rating that measures how much warmth a fabric traps. The higher the number, the more insulation it provides. Most sleep sacks list a TOG rating on the packaging, which makes matching the sack to your room temperature straightforward. A 0.5 TOG sack is barely more than a sheet, while a 2.5 TOG sack feels like a light quilt.
If you own two sleep sacks (a 0.5 or 1.0 for warmer months, a 2.5 for cooler ones), you’re covered for the entire year. You don’t need a different sack for every five-degree shift in temperature. Layer the clothing underneath up or down instead.
Choosing the Right Fabric
Cotton is the most common choice for baby sleepwear, and for good reason: it’s soft, breathable, and widely available. Organic cotton avoids pesticide residues. The downside is that cotton absorbs moisture and holds it against the skin rather than pulling it away, which can feel clammy on humid nights.
Bamboo fabric runs about 20% more breathable than cotton and naturally wicks moisture, staying roughly three degrees cooler to the touch. It also regulates temperature across seasons, making it a strong pick if you want one set of pajamas that works year-round. The tradeoff is cost: bamboo garments tend to be pricier.
Muslin works well for swaddles and lightweight layers because of its open weave and quick drying time, but it loses shape faster in structured garments like onesies. Linen conducts heat away from the body efficiently, though its rougher texture isn’t ideal against newborn skin.
Swaddling: When to Start and Stop
Swaddling can help newborns feel secure in the first weeks of life, but it comes with a hard deadline. You need to stop swaddling as soon as your baby shows any signs of trying to roll over. Some babies start working on rolling as early as two months, though the more typical window is three to four months. A swaddled baby who rolls onto their stomach faces a serious suffocation risk because they can’t use their arms to reposition.
Once you stop swaddling, a sleep sack is the natural next step. Arms-free sleep sacks give your baby full use of their hands and arms while still providing warmth. There’s no evidence that swaddling reduces the risk of SIDS, so if your baby doesn’t seem to like it, skipping it entirely is perfectly fine.
Weighted swaddles, weighted sleep sacks, and any weighted objects placed on or near a sleeping baby are not recommended. The AAP specifically advises against them.
No Hats Indoors
This surprises a lot of new parents, especially in winter. Babies should not wear hats while sleeping indoors. Hats trap heat, and since babies release excess warmth through their heads, covering it can lead to overheating quickly. The only exception is the first few hours after birth or in a NICU setting. At home, skip the hat entirely for sleep.
How to Check if Your Baby Is Too Warm
The best spot to check is your baby’s chest or the back of their neck. Place your hand there. If the skin feels hot or damp, your baby is overdressed. Don’t rely on their hands and feet, which often feel cool even when the rest of their body is perfectly warm.
Signs of overheating include flushed or red skin, sweating or damp hair, fussiness, and unusual lethargy. A baby who seems sluggish, listless, or overly tired may be too warm rather than just sleepy. Some babies overheat without sweating at all, so skin temperature is a more reliable check than visible perspiration. Overheating is an independent risk factor for sleep-related infant deaths, which is why erring on the slightly cooler side is safer than piling on extra layers “just in case.”
Putting It All Together
A practical nightly routine looks like this: check the room temperature, pick a bodysuit that matches the warmth level, and zip your baby into the appropriate sleep sack. No loose blankets, no hats, no weighted products. Keep the crib bare. If you’re unsure whether you’ve got the layers right, do a chest check about 15 minutes after putting your baby down. Warm but dry skin means you nailed it. Hot or sweaty skin means remove a layer. Cool skin on the torso (not just the hands) means add one.
Running a fan on low in the nursery helps circulate air and has been associated with a more comfortable sleep environment. It doesn’t need to blow directly on your baby. Just keep the air moving gently in the room.