Newborns should sleep in one layer more than what you’re comfortably wearing, with no loose blankets, hats, or heavy coverings. For most homes, that means a simple onesie or bodysuit under a sleep sack or swaddle. The goal is keeping your baby warm enough without overheating, which is a known risk factor for SIDS.
The One-Layer Rule
The simplest guideline comes from both the American Academy of Pediatrics and the NHS: dress your baby in one extra layer compared to what feels comfortable for you. If you’re fine in a t-shirt and light sweater, your baby does well in a bodysuit, a footed sleeper, and a sleep sack or light blanket layer on top. If you’re comfortable in just a t-shirt, your baby likely only needs a bodysuit and a lightweight sleep sack.
This rule scales naturally with the seasons. It also prevents the common mistake of overdressing, which parents tend to do more often than underdressing. Babies lose heat through their heads and regulate temperature less efficiently than adults, but that doesn’t mean they need to be bundled up heavily indoors.
Room Temperature Guides Everything
The recommended room temperature for sleeping babies is 61 to 68°F (16 to 20°C). What your baby wears depends directly on where your room falls in that range.
- Below 61°F (16°C): A long-sleeve bodysuit under a footed sleeper, plus a higher-warmth sleep sack. Don’t pile on extra blankets over a sleep sack. Instead, add a clothing layer underneath or switch to a warmer sack.
- 61 to 68°F (16 to 20°C): A bodysuit under a footed sleeper with a standard sleep sack works well for most babies.
- 68 to 75°F (20 to 24°C): A short-sleeve bodysuit with a lightweight sleep sack, or a footed sleeper alone.
- Above 75°F (24°C): A short-sleeve bodysuit or even just a diaper is fine. In genuinely hot weather, less really is more.
A common mistake is doubling up on sleep sacks or blankets to compensate for a cold room. Air gets trapped between layers and increases warmth beyond what you’d expect. Two 1.0-tog layers don’t simply add up to 2.0 tog; they can create dangerous heat buildup.
Understanding TOG Ratings
Many sleep sacks list a TOG rating, which measures thermal resistance (how much warmth the fabric holds in). Higher numbers mean warmer garments. Here’s a quick guide:
- 0.2 TOG: For rooms 75 to 81°F. Barely more than a sheet.
- 1.0 TOG: For rooms 68 to 75°F. A good all-purpose weight.
- 2.5 TOG: For rooms 61 to 68°F. Suitable for cooler bedrooms in winter.
- 3.5 TOG: For rooms below 61°F. The warmest option available.
If your home temperature fluctuates, having two sleep sacks in different weights lets you adjust without changing the whole outfit.
Sleep Sacks, Swaddles, and When to Switch
Loose blankets, quilts, comforters, and sheepskins are not safe in a baby’s sleep space. Even lightweight blankets that are tucked in can work free and cover a baby’s face. The safest crib has nothing in it except a fitted sheet on a firm mattress.
Swaddling is fine for young newborns who haven’t started trying to roll. A proper swaddle keeps arms snug but leaves enough room at the hips for natural movement and doesn’t restrict breathing. The critical rule: stop swaddling as soon as your baby shows any signs of trying to roll over, which can happen as early as 2 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, transition to a sleep sack that leaves the arms free. These non-swaddling wearable blankets can be used for as long as you’d like, since they don’t restrict movement. Weighted swaddles, weighted sleep sacks, and weighted blankets of any kind are not recommended at any age.
No Hats Indoors
Babies often come home from the hospital wearing a hat, which makes sense in a drafty delivery room. But once you’re home, remove the hat for sleep. Hats can cause overheating and, if they slip, create a suffocation risk. Research from neonatal intensive care units found that even premature babies in open cribs maintained normal body temperature without hats. The recommendation applies to all infants sleeping indoors.
Best Fabrics for Baby Sleepwear
Cotton is the most widely available and affordable option. It’s soft, breathable, and familiar. Its main limitation is that it absorbs moisture and holds it against the skin rather than wicking it away, so it can feel clammy on sweaty babies or in humid conditions.
Bamboo fabric is roughly 20% more breathable than cotton and stays about 2 to 3 degrees cooler against the skin. It actively wicks moisture away rather than holding it, making it a strong choice for babies who run warm or for summer months. Bamboo is also naturally hypoallergenic, which can help if your baby has sensitive or eczema-prone skin.
Muslin, with its open weave, offers excellent airflow and dries quickly. It works well for lightweight summer sleepwear but tends to lose its shape faster with repeated washing. For a structured garment like a sleeper or sleep sack, cotton or bamboo holds up better over time.
How to Check if Your Baby Is Too Hot or Cold
The most reliable 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, remove a layer. If it feels cool, add one. Your baby’s hands and feet will almost always feel cooler than the rest of their body, so don’t use them as your guide.
Signs of overheating include flushed or red skin, sweating, damp hair, unusual fussiness, or unusual sleepiness. Some overheated babies sweat visibly; others don’t. If your baby’s chest feels hot to the touch, that’s your signal regardless of whether you see sweat. Overheating is a modifiable risk factor for SIDS, which means it’s one of the things you can directly control.
Putting It All Together
For a typical home kept around 68 to 72°F, a solid starting outfit is a short- or long-sleeve bodysuit (depending on the season) under a 1.0-tog sleep sack. No hat, no loose blankets, no extra padding. Check your baby’s chest after 10 to 15 minutes to see if you’ve hit the right balance. Over a few nights, you’ll develop a feel for what combination works in your specific home. If you’re comfortable in a t-shirt in the nursery, your baby is likely comfortable in a onesie and a light sleep sack.