Dress your newborn in one layer more than what you’re comfortable wearing, and skip the loose blankets entirely. For most homes kept between 68 and 72°F, that typically means a onesie underneath a sleep sack or wearable blanket. Getting this right matters more than many parents realize: overheating during sleep is a known risk factor for SIDS, and babies can’t regulate their own body temperature the way adults can.
The One-Layer Rule
The simplest guideline is to give your baby one extra layer compared to what you’d wear comfortably in the same room. If you’re sleeping in a t-shirt and feel fine, your baby needs a short-sleeve onesie plus a light sleep sack. If the room is cool enough that you’d want a sweatshirt, add a footed sleeper under a warmer sleep sack.
This rule works because newborns lose heat faster than adults due to their large head-to-body ratio and thin skin, but they also can’t cool themselves down efficiently by sweating. One extra layer keeps them warm without trapping excess heat.
What Counts as Safe Sleepwear
Safe options include fitted onesies, footed sleepers (also called “footie pajamas”), and wearable blankets or sleep sacks. These stay close to the body and don’t ride up over your baby’s face. You can layer a onesie or bodysuit underneath a sleep sack depending on the room temperature.
What’s not safe: loose blankets, quilts, comforters, or any unfitted bedding in the crib. These increase the risk of suffocation and strangulation. Weighted blankets, weighted swaddles, and weighted sleepers are also off limits. And once you’re home from the hospital, don’t put a hat on your baby for indoor sleep. Babies release excess heat through their heads, so covering it can cause overheating.
Swaddling and When to Stop
Swaddling works well for newborns who startle themselves awake, but it comes with specific rules. The swaddle should be snug around the arms and chest but loose enough around the hips that your baby can bend and move their legs freely. A too-tight swaddle can interfere with hip development. Always place a swaddled baby on their back.
The critical cutoff: stop swaddling as soon as your baby shows any signs of trying to roll over. Some babies start working on rolling as early as 2 months. Once rolling begins, a swaddle becomes dangerous because your baby could end up face-down without free arms to reposition. At that point, switch to a sleep sack that leaves the arms free. Unswaddled sleep sacks with open arms can be used for as long as you want.
Room Temperature and TOG Ratings
Keep the nursery between 68 and 72°F. This range is warm enough for a lightly dressed baby in a sleep sack and cool enough to avoid overheating. A simple room thermometer near the crib takes the guesswork out of it.
If you’re shopping for sleep sacks, you’ll see something called a TOG rating, which measures thermal resistance (essentially, how warm the fabric keeps your baby). Here’s a practical breakdown:
- 0.2 TOG: Very lightweight, best for warm rooms between 75°F and 81°F. Think single-layer muslin.
- 1.0 TOG: The most versatile option, suited for rooms between 68°F and 75°F. This is the sweet spot for most nurseries.
- 2.5 TOG: A warmer option for cooler rooms between 61°F and 68°F, like drafty older homes in winter.
- 3.5 TOG: The warmest available, for rooms below 61°F.
A 1.0 TOG sleep sack over a long-sleeve onesie handles the typical nursery well. In summer or warmer climates, drop to a 0.2 TOG sack with just a diaper or a short-sleeve bodysuit underneath.
Best Fabrics for Baby Sleep
Cotton and cotton muslin are the go-to choices for sleepwear. They’re breathable, allowing air to circulate so heat doesn’t get trapped against your baby’s skin. Jersey knit cotton has similar properties and tends to be softer and stretchier, which makes it comfortable for overnight wear. Bamboo-blend fabrics are another good option, as they wick moisture and help regulate temperature.
Fleece and flannel retain more heat, which makes them useful in genuinely cold rooms but risky if your nursery is already at a comfortable temperature. Polyester is less breathable than natural fibers and is best avoided for sleepwear, especially in warmer months. If you’re unsure, cotton is almost always the right call.
Why Overheating Is Dangerous
Overheating isn’t just uncomfortable for babies. It’s a genuine safety concern. When a young infant gets too warm during sleep, the thermal stress can interfere with their ability to wake up, breathe normally, and regulate their heart rate. These are all protective mechanisms that are still developing in the first year of life. Research published through the National Institutes of Health found that a 10°F increase in daily temperature during summer months was associated with an 8.6% increased risk of SIDS.
This risk is higher for babies between 3 and 11 months old, who showed a 16.9% increased SIDS risk per 10°F temperature rise in summer, compared to 2.7% for younger infants. The takeaway isn’t to panic about warm days, but to pay attention to how warm your baby is when they sleep, especially during heat waves or in homes without air conditioning.
How to Check if Your Baby Is Too Warm
Don’t rely on your baby’s hands or feet, which are often cool even when the rest of the body is perfectly warm. Instead, touch the back of their neck or their chest. If the skin there feels hot, sweaty, or clammy, they’re overdressed.
Other signs of overheating include flushed or red skin, damp hair, unusual fussiness, or sluggishness. Babies can overheat without visibly sweating, so skin temperature is a more reliable check than looking for sweat. If your baby seems too warm, remove a layer, lower the room temperature, or switch to a lighter sleep sack.
Dressing for Different Seasons
In summer, a diaper with a lightweight 0.2 TOG sleep sack is often enough. If the room stays below 75°F with air conditioning, a short-sleeve bodysuit under a 1.0 TOG sack works well. Avoid the temptation to skip the sleep sack entirely and use a blanket instead, no matter how thin.
In winter, start with a long-sleeve onesie or footed sleeper and add a 1.0 to 2.5 TOG sleep sack depending on how cold the room gets overnight. If your home drops below 65°F, a footed sleeper under a 2.5 TOG sack provides warmth without loose bedding. Resist the urge to pile on layers. If you find yourself adding more than two layers plus a sleep sack, the room itself is too cold and needs to be warmed rather than compensating with extra clothing.
For transitional weather in spring and fall, the room temperature can swing significantly between bedtime and early morning. A 1.0 TOG sleep sack with a bodysuit underneath gives you a safe middle ground. Check your baby’s chest temperature during a nighttime feeding to see if adjustments are needed.