For most nurseries kept between 68°F and 72°F, a cotton onesie underneath a lightweight sleep sack is the right combination. The exact setup depends on your room temperature, your baby’s age, and the thickness of the sleep sack you choose. Getting this right matters more for babies than for adults, because infants are significantly less efficient at regulating their own body temperature. Their sweat response is underdeveloped, especially in the first few months, which means they can overheat or get too cold without showing obvious signs right away.
A simple rule of thumb: dress your baby in one layer more than what you’d wear to sleep comfortably in the same room.
Start With Your Room Temperature
Room temperature is the single biggest factor in deciding what your baby wears to bed. The ideal range for a nursery is between 68°F and 72°F (20°C to 22°C). If your room falls outside that window, you’ll adjust layers up or down accordingly. A cheap room thermometer near the crib is more reliable than guessing, and temperatures can shift overnight, especially in older homes or rooms with large windows.
Here’s how room temperature maps to clothing:
- 75°F to 81°F: A single short-sleeve onesie or just a diaper with a very thin (0.2 TOG) sleep sack.
- 68°F to 75°F: A long-sleeve cotton onesie with a lightweight (1.0 TOG) sleep sack.
- 64°F to 68°F: A long-sleeve onesie or cotton pajamas with a mid-weight (1.5 to 2.5 TOG) sleep sack.
- Below 61°F: A thermal onesie or footed pajamas under a heavy (3.5 TOG) sleep sack.
What TOG Ratings Mean
TOG stands for Thermal Overall Grade, and it measures how much warmth a fabric traps. The higher the number, the warmer the garment. A 0.2 TOG sleep sack is barely more than a single layer of muslin. A 2.5 TOG feels like a light blanket. Most families in climate-controlled homes will use a 1.0 TOG sleep sack for the majority of the year and keep a 2.5 TOG on hand for winter.
The TOG rating accounts for the sleep sack alone, not the clothing underneath. That’s why you layer a onesie or pajamas beneath it and adjust based on the room. If your baby is wearing thick footed pajamas under a high-TOG sleep sack, you may be adding more warmth than you realize.
Swaddles, Sleep Sacks, and When to Switch
Newborns from birth to roughly two to three months often sleep in a swaddle, which wraps snugly around their arms and torso. Swaddling helps dampen the startle reflex that wakes young babies. But the moment your baby starts showing signs of rolling over, the swaddle needs to go. For some babies this happens as early as eight weeks; for others it’s closer to six months. Signs include pushing up during tummy time, lifting their legs and flopping them to one side, or breaking free from the swaddle repeatedly.
Rolling while swaddled is dangerous because a baby on their stomach with their arms pinned can’t push themselves back over, which can restrict breathing. The transition from swaddle to sleep sack is the standard next step. Sleep sacks leave the arms free while still providing warmth without loose blankets in the crib. Many families use sleep sacks well into toddlerhood.
What Not to Use
Loose blankets, pillows, and stuffed animals do not belong in the crib. The AAP recommends a flat, firm sleep surface with nothing else on it. This applies through at least the first year.
Weighted sleep sacks and weighted swaddles are also off the table. The AAP and the Consumer Product Safety Commission both advise against them. These products have been linked to reduced oxygen levels in infants, and major retailers have begun pulling them from shelves. No matter how calming the marketing sounds, the risk is real.
Hats and beanies should not be worn indoors during sleep. Babies release excess heat through their heads, so covering it interferes with temperature regulation. The only exception is in the first hours after birth or in a NICU setting.
Choosing the Right Fabric
Cotton is the default for baby sleepwear, and it works well. It’s soft, widely available, and breathable. The downside is that cotton holds onto moisture longer, so if your baby sweats, the fabric stays damp against their skin.
Bamboo fabric has become a popular alternative. The fibers have natural micro-gaps that allow better air circulation, making bamboo about 2 to 3 degrees Celsius cooler than cotton in warm conditions. It also wicks moisture away from the skin more effectively, which is particularly helpful for babies prone to eczema or heat rash. Bamboo’s moisture-wicking properties help prevent the dampness that can trigger skin flare-ups.
Either fabric works. In warmer climates or for babies who run hot, bamboo has a measurable edge. In moderate, climate-controlled rooms, cotton is perfectly fine.
How to Tell if Your Baby Is Too Hot or Too Cold
Hands and feet are unreliable indicators. Babies naturally have cooler extremities, so cold fingers don’t necessarily mean your baby needs another layer. Instead, touch the back of their neck or their chest. If the skin there feels hot, sweaty, or clammy, they’re overdressed. If it feels cool to the touch, they may need an extra layer.
Signs of overheating include flushed or red skin, damp hair, fussiness, and restlessness. In more serious cases, a baby may become unusually sluggish or lethargic. It’s worth noting that babies can overheat without visibly sweating, especially younger infants whose sweat glands aren’t fully developed. Babies born at full term can sweat from birth, but the efficiency of that sweating as a cooling mechanism is poor in the early weeks.
Overheating is a bigger concern than being slightly cool. A baby who is a little chilly will fuss and wake you up. Overheating is a known risk factor for sleep-related dangers and often goes unnoticed longer.
Putting It All Together
For a typical nursery at 68°F to 72°F, the setup most families land on is a long-sleeve cotton or bamboo onesie under a 1.0 TOG sleep sack. No hat, no socks (the sleep sack covers the feet), no blankets. For newborns under two to three months who aren’t yet rolling, a 0.5 TOG swaddle over a single cotton onesie works in that same temperature range.
If your home runs warm in summer, strip down to a short-sleeve onesie or just a diaper with a 0.2 TOG sack. If your nursery dips into the low 60s in winter, move up to footed pajamas under a 2.5 TOG sack. Check their chest or neck about 20 minutes after putting them down to see how they’re actually doing, and adjust from there. After a few nights, you’ll have a reliable setup dialed in for your home.