What Should Babies Wear Under Sleep Sack

What should babies wear under sleep sack is a common question among most parents whose babies don’t like to be covered at night.

Sleepsacks like the Halo SleepSack Wearable blanket or SwaddleMe are a great replacement to loose blankets, especially during cold nights. They are quite flexible in that they can be layered with the right clothing to keep babies warm and cozy.

For instance, it is perfectly okay for a baby to wear an onesie under a sleep sack in moderate temperatures in the nursery. At room temperature, you can dress the baby in a short-sleeved onesie, a footless romper, and a sleep sack to keep them warm.

What should babies wear under sleep sack

However, care must be taken when deciding on what a baby should wear underneath a sleep sack depending on whether it is in summer or winter. This is because if underdressed they may have a hard time sleeping because they are cold and if overdressed, they may overheat.

In this article, we shall look at the different factors that you should consider when choosing what your baby should wear under the sleep sack and the appropriate clothing you can use for layering.

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What should babies wear under sleep sack at night?

What you choose will be influenced by different factors such as the temperature in the nursery, the material of the sleep sack, and the TOG value of the sleep sack.

Nursery temperature

Professionals explain that what you choose for layering should depend on the temperature in your house.

For instance, if the temperature is about 75 degrees Fahrenheit, a short-sleeved onesie under the sleep sack would be enough.

However, if the temperature is a bit lower like 64 degrees Fahrenheit, then a long-sleeved onesie such as Carter Baby Boy’s or Hudson Baby Girls onesies coupled with a footless romper, can be worn under the sleep sack to keep the baby warm.

What should babies wear under sleep sack

Most parents choose to have the thermostat at home or in the nursery set between 69 to 72 degrees Fahrenheit. Although this is considered the perfect temperature for sleep, it might still be a little bit cold for your baby and he may need extra layering. Therefore, according to the table below, you should add a short-sleeved onesie and a footless romper under the sleep sack.

Here is a table to help you choose the most suitable clothing for your baby to sleep in at different temperatures.

What should babies wear under sleep sack
Photo courtesy of sleeperific.com

TOG value of the sleeping bag

Another important factor to consider is the TOG value of your baby’s sleep sack.

TOG simply refers to a measure of thermal insulation or thermal effectiveness of a blanket or sleep sack. In short, TOG indicates how well a blanket or sleep sack can keep a baby warm.

You determine the most suitable TOG of your baby’s sleep sack based on the temperature in the nursery.

From the image we have provided above, you can see those different temperatures require different TOG sleeping bags and layering.

A sleep-sack with a TOG of 0.5 is best suited for warmer temperatures such as summer since it is light and breathable. It can be layered with an onesie if the temperatures are about 75-770 F.

TOG 1 sleep sacks are meant for moderate temperatures since they have some sort of insulation and yet breathable. Ideally, they can be worn all year round since they are very comfortable in cold or hot weather. However, you need the right amount of layering depending on temperature.

A sleeping bag with 2.5 TOG is the most appropriate for chilly and cold nights such as in winter. If the temperature in the nursery is under 600F, you should dress your baby warmly by adding extra clothing such as a footless romper, long-sleeved onesie, mittens, socks, and a hat.

Therefore, lower temperature requires a higher TOG sleep sack and more extra clothing in order to keep the baby warm.

See also: Best crib tents

Sleep sack material–fleece or cotton?

The material of the sleep sack is also an important factor to take into account.

All sleep sack materials are designed to be breathable and draw off moisture to prevent overheating. However, the materials differ based on their thermal effectiveness or insulation.

how to dress baby for sleep under sleep sack

Cotton fabric tends to be more breathable and lighter compared to fleece. This means that on a chilly night, your baby may feel colder in a cotton sleep sack and warmer in a fleece one. Hence, a cotton sleep sack would need more layering to ensure the baby is warm and cozy.

In one of the parenting forums, a mom stated;

“My son cannot wear any fleece because he would boil in it but he is perfectly okay in a cotton sleeping bag”.

However, when it comes to layering, you must consider the temperature in the nursery. This will help to prevent overdressing the baby or underdressing him.

Related article: Best Huggies Pull-Ups

FAQ about what should babies wear under sleep sack

Q1. Should a baby wear an onesie under a sleeper?

Yes, it is perfectly okay for a baby to wear an onesie under a sleep sack. It is actually the best way to keep a baby warm in moderate temperatures in the nursery.

how to dress baby in summer

However, if it is too cold then you may need to add more layers of clothing along with the onesie but reduce the layers in case it is too hot.

Q2. Are weighted sleep sacks safe for babies?

Sleep sacks are generally considered a safer option than blankets. However, not all weighted sleep sacks are safe.

The American Academy of Pediatrics (AAP) recommends parents to use only approved sleep sacks such as the Nested Bean, which is considered safe for babies.

Q3. Can baby overheat in a sleep sack?

One thing that causes a baby to overheat in a sleep sack is overdressing.

You may be tempted to add more clothing under the sleep sack especially when it is chilly. But, before doing this, consider the 3 factors we have discussed above; the temperature in the nursery, TOG of the sleep sack, and the material. These factors will help you choose suitable clothing for your baby.

Q4. How to dress baby for sleep in 70 degree room (21 degrees Celsius)

Temperature between 68 and 72 degrees Fahrenheit is considered safe for the baby to prevent the risk of SIDS according to the American Academy of Pediatrics.

Thus, 70 degrees is considered to be room temperature. This may be a little cold for your baby and therefore you may need to add a few layers of clothing under the sleep sack.

Dressing baby for sleep

Ideally, dress the baby in a short-sleeved onesie, a footless romper, and a sleep sack to ensure they are warm and cozy through the night.

Q5. How to dress baby in a sleep sack at 75 degrees Fahrenheit (24 degrees Celsius)

In summer, the temperature may go over 75 degrees Fahrenheit, which is a bit too hot. Therefore, you need to ensure that your baby is not overdressed as this may lead to overheating.

Appropriate clothing for baby at this temperature would be a short-sleeved onesie under a sleep sack.

Another tip that parents use to determine how to dress a baby is to add one more layer of clothing than you are wearing in the same environment.

See also: Best nursery curtains


When it comes to dressing your baby for sleep, you should be careful not to underdress or overdress them. Overdressing leads to overheating and increases the risk of Sudden Infant Death (SIDS). So if you are wondering what should babies wear under sleep sack; you need to consider a few things.

You must take into account the temperature in the nursery, the material of the sleep sack, and its TOG value.

Basically, if the temperature is high, make sure that the baby dresses in a low TOG sleep sack preferably made of light and breathable cotton. In this case, the extra clothing maybe just an onesie.

Conversely, if the temperature is low, dress the baby in a high TOG sleep sack that is preferably made of fleece since it is well insulated. Extra layering may include a footless romper, an onesie, socks, and hat depending on how cold it is.

Sophie Moore

Last update on 2021-01-18 at 17:35 / Affiliate links / Images from Amazon Product Advertising API

One Comment

  1. Oh, my! I remember how scared and confused I was when I had my first baby girl. I was always questioning myself – am I doing it right? Am I dressing her enough? Or is it too much 😀 Being a parent for the first time is not easy, so it is nice to have good sources of information like this article. The infographic with the temperatures and the clothes are a treasure!

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