At 70°F (21°C), your baby needs about one layer plus a lightweight sleep sack. This is a comfortable middle-ground temperature for infant sleep, so you don’t need to overthink it. A long-sleeve cotton onesie paired with a 1.0 TOG sleep sack is a solid starting point, and you can adjust from there based on how your baby feels.
The Basic Setup at 70 Degrees
The general rule from the American Academy of Pediatrics is that babies need one more layer than you would wear in the same environment. At 70°F, most adults are comfortable in a single layer, so your baby does well in a light base layer plus a wearable blanket.
For a room that stays around 69 to 74°F, a cotton onesie (long or short sleeve) under a sleep sack with a TOG rating of 1.0 is the go-to combination. TOG is a measure of thermal resistance, essentially how much warmth a fabric traps. A 1.0 TOG sleep sack is designed for room temperatures between 68°F and 75°F, making it a natural fit for a 70-degree nursery. If your baby tends to run warm, go with a short-sleeve bodysuit underneath. If they run cool, opt for long sleeves or lightweight footed pajamas.
For younger babies still in a swaddle, the same temperature range calls for a swaddle rated at 2.0 TOG or less, paired with long- or short-sleeve cotton pajamas underneath. Swaddles trap more warmth between the fabric and your baby’s body, so you may need a thinner base layer compared to a sleep sack.
What to Put Under the Sleep Sack
The layer beneath the sleep sack matters more than people realize, because the heat trapped between layers adds up quickly. At 70°F, you have a few combinations that work:
- Short-sleeve bodysuit + 1.0 TOG sleep sack: Good for babies who sleep warm or rooms that creep above 70°F overnight.
- Long-sleeve bodysuit + 1.0 TOG sleep sack: The most common setup for a steady 70°F room.
- Footed pajamas + 1.0 TOG sleep sack: Better if the room dips into the mid-60s by early morning.
- Footed pajamas alone, no sleep sack: Works if your baby is older and consistently warm at night.
There’s no universal chart that matches exact temperatures to exact outfits, because every product is made from different materials with different thermal properties. The Lullaby Trust, a leading safe sleep organization, specifically notes that they can’t provide one-size-fits-all layering advice for this reason. Your best guide is your baby’s actual body temperature, checked by touch.
How to Tell If Your Baby Is Too Warm or Too Cold
The most reliable spot to check is the back of your baby’s neck or their chest. These areas reflect core body temperature better than hands or feet, which tend to run cool naturally. If the skin there feels warm and dry, your baby is comfortable. If it feels hot, clammy, or sweaty, they’re overdressed.
Signs of overheating include flushed or red skin, damp hair, fussiness, restlessness, or unusual sluggishness. Some babies sweat visibly when they’re too warm, but others overheat without sweating at all, so don’t rely on sweat alone. Cheeks, ears, and the neck area that feel noticeably hot are a more consistent signal. Overheating is more than just a comfort issue. The AAP warns that it increases the risk of SIDS, so erring on the slightly cool side is safer than bundling too much.
Skip the Hat Indoors
Babies lose excess heat through their heads, which is actually a feature, not a problem, when they’re sleeping indoors. A study of neonatal intensive care units found that removing hats from infants sleeping in open cribs did not cause temperature problems. Only 2.7% of infants became mildly hypothermic, and those were fragile NICU babies in a hospital setting. For a healthy baby in a 70-degree home, a hat during sleep adds unnecessary warmth and a potential suffocation risk if it slips down. Hats are for outdoor trips, not the crib.
Choosing the Right Fabric
Cotton is the classic choice for baby sleepwear, and for good reason: it’s breathable, affordable, and widely available. At 70°F, a lightweight cotton onesie does the job well. Bamboo viscose is another popular option that’s 40% more absorbent than organic cotton and wicks moisture faster. The natural micro-structure of bamboo fibers allows more airflow than cotton, which can be helpful for babies who tend to sweat at night. Both fabrics work fine at this temperature range.
Fleece and polyester blends trap more heat, so they’re better suited for colder rooms (below 65°F) or as a sleep sack material rather than a base layer. At 70 degrees, fleece pajamas under a sleep sack would likely push your baby into overheating territory.
When the Temperature Shifts Overnight
A room that reads 70°F at bedtime might drop to 65°F by 3 a.m. or climb a few degrees if you’re running heat. If you know your home cools significantly overnight, dress for the lower end of the range: a long-sleeve onesie with a 1.0 TOG sleep sack, or footed pajamas with the sack. This gives your baby a buffer without overheating them at bedtime.
If your room tends to warm up overnight, go lighter. A short-sleeve bodysuit with a 1.0 TOG sack, or even just footed pajamas without a sack, keeps your baby from getting too hot in the early morning hours. A simple room thermometer near the crib (not by a window or vent) helps you track patterns over a few nights so you can dial in the right combo.
Most sleep sack manufacturers include a temperature guide on the packaging or their website, matched to the specific TOG rating of that product. These guides are worth checking, since the materials vary enough between brands that a 1.0 TOG sack from one company may feel warmer than another. Follow the manufacturer’s guidance and then verify with a quick touch check on your baby’s chest or neck before you go to bed.