The safest approach to dressing a baby for sleep is one fitted layer plus a sleep sack, adjusted based on room temperature. The ideal nursery temperature is 68 to 72°F (20 to 22°C), and most babies sleep comfortably in that range with a long-sleeve onesie and a lightweight sleep sack. Getting this right matters because overheating is a known risk factor for SIDS.
Start With Room Temperature
Before choosing what your baby wears, check the room. A thermometer in the nursery is more reliable than guessing. The recommended range is 68 to 72°F (20 to 22°C). The NHS advises keeping the room between 61 and 68°F (16 to 20°C) for safe sleep, which is slightly cooler than most American homes. Either range works as long as you adjust what your baby wears accordingly.
If your home runs warm in summer or you can’t control the temperature precisely, dress lighter. In really hot weather, a short-sleeve bodysuit or even just a diaper is fine. If your home is cooler, add a layer of clothing underneath the sleep sack rather than piling on extra blankets.
What to Dress Baby In, by Temperature
There’s no single universal chart that works for every baby and every product, because fabric thickness and material vary between brands. The Lullaby Trust, a leading UK infant sleep charity, notes that the heat trapped between layers changes insulation significantly, making one-size-fits-all charts unreliable. That said, here are general guidelines:
- 75°F and above (24°C+): A short-sleeve bodysuit or just a diaper. If using a sleep sack, choose the thinnest option available (0.2 TOG).
- 68 to 75°F (20 to 24°C): A long-sleeve onesie or footed pajamas with a lightweight sleep sack (0.5 to 1.0 TOG).
- 61 to 68°F (16 to 20°C): A long-sleeve onesie under footed pajamas, paired with a midweight sleep sack (1.5 to 2.5 TOG). Or a single layer with a warmer sleep sack.
- Below 61°F (16°C): An extra base layer under pajamas with a warm sleep sack (2.5 to 3.5 TOG).
The key principle: add or remove layers of clothing rather than stacking blankets or doubling up sleep sacks. Air gets trapped between layers, which increases warmth in ways that are hard to predict. Two 1.0 TOG sleep sacks worn together do not equal 2.0 TOG. They can trap enough heat to be dangerous.
What TOG Ratings Mean
TOG is a measure of thermal resistance, essentially how warm a fabric keeps your baby. The higher the number, the more insulating the garment. Most sleep sack brands print the TOG rating on the label and include a temperature guide. Here’s what the numbers translate to in practice:
- 0.2 TOG: Very lightweight, almost like a sheet. For rooms 75 to 81°F.
- 1.0 TOG: Light warmth. For rooms 68 to 75°F.
- 2.5 TOG: Moderate warmth. For rooms 61 to 68°F.
- 3.5 TOG: Heavy warmth. For rooms below 61°F.
Follow the manufacturer’s guide for the specific sleep sack you own, since the actual warmth depends on the fabric blend and construction. Having two or three sleep sacks in different weights covers you across seasons.
Choosing the Right Fabric
Natural fibers generally breathe better than synthetics, which helps prevent overheating. Cotton is the most common and widely available choice for baby sleepwear. It’s breathable, soft, and washes well.
Bamboo-based fabrics have strong moisture-wicking properties, pulling sweat away from skin and keeping it dry. This can be especially helpful for babies prone to eczema or rashes, since damp skin worsens those conditions. Merino wool is another option with an unusual property: its fiber structure creates tiny air pockets that trap warmth in cold conditions but allow cooling through evaporation in warm conditions. It naturally regulates temperature in both directions, which makes it forgiving if the room temperature fluctuates overnight. It’s pricier than cotton or bamboo, but some parents find it worth the investment for winter months.
Polyester and synthetic blends tend to trap heat and moisture. They’re not dangerous, but they’re less forgiving if your baby runs warm.
How to Tell If Your Baby Is Too Hot or Cold
Your baby’s hands and feet are not reliable indicators. Cool hands and slightly bluish fingers are normal in healthy infants and don’t mean your baby is cold. Instead, place your hand on your baby’s chest or the back of their neck. That’s where you’ll get an accurate read on their core temperature.
If their chest feels hot or their skin is sweaty, they’re overdressed. Remove a layer. If their chest feels cool to the touch, add one. You’ll likely check a few times during the first nights in a new sleep setup, and then you’ll develop a sense of what works for your home’s temperature.
Signs of overheating include flushed cheeks, rapid breathing, sweating, damp hair, and restless sleep. Overheating is more common than parents expect, partly because the instinct to bundle a baby up is strong. When in doubt, go lighter rather than heavier.
What Not to Use
The CDC and AAP guidelines are clear: keep soft bedding out of the sleep area entirely. That means no loose blankets, pillows, bumper pads, or stuffed animals in the crib. A properly sized sleep sack replaces a blanket safely.
Do not cover your baby’s head during sleep. Hats should come off as soon as you’re indoors, even if that means waking your baby. Babies lose excess heat through their heads, and covering it interferes with temperature regulation. The same applies after car rides or stroller trips. Remove hats, extra jackets, and bunting suits when you come inside or board heated transportation.
Babies should never sleep next to a radiator, heater, or heat source, and should never use hot water bottles or electric blankets.
Socks, Mittens, and Footed Pajamas
Newborn mittens are rarely needed. Cool hands are normal and don’t bother your baby, even though they might worry you. Many hospitals now discourage mitten use because mittens limit the sensory feedback babies get from touching things, which supports early neurological development.
Socks are fine if your baby’s pajamas don’t have feet, but they often fall off and end up loose in the crib. Footed pajamas solve this problem neatly. In warm weather, footless pajamas or a bodysuit with bare feet keeps things simple.
Swaddling and When to Stop
Swaddling works well for many newborns because it dampens the startle reflex that wakes them. But you need to stop swaddling as soon as your baby shows signs of rolling over. This can happen as early as 8 weeks, though most babies start showing these signs between 2 and 6 months.
Watch for these cues during awake time: rolling to one side during play, pushing up on hands during tummy time, lifting legs and flopping them sideways, or consistently breaking free from the swaddle. Once you see any of these, it’s time to transition to a sleep sack with arms free. A swaddled baby who rolls onto their stomach cannot push themselves back over, which creates a suffocation risk.
Transitional sleep sacks with arm openings can ease the shift. Some babies adjust in a night or two, others take a week. The startle reflex typically fades around the same age, so the transition often goes more smoothly than parents expect.
Practical Layering Tips
The simplest system is a base layer (bodysuit or onesie) plus a sleep sack in the right TOG for your room. Two pieces, easy to adjust. If the room is warm, drop the base layer and put your baby in the sleep sack in just a diaper. If it’s cold, swap the short-sleeve bodysuit for a long-sleeve one, or add footed pajamas as a middle layer.
Keep a room thermometer in the nursery and check it at bedtime. Room temperatures often drop overnight, especially in spring and fall when heating cycles off. If your home swings more than a few degrees, dress for the coolest point of the night and your baby will self-regulate through the warmer hours. Checking your baby’s chest temperature once before you go to bed gives you confidence that the setup is working.