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Dressing your baby for bed can be a stress-inducing experience. You want her to be warm but not too warm, cool but not too cool. You have your sleep sack ready, along with a onesie, footed pajamas, a hat, and mittens. But what should a baby wear under a sleep sack?

Sleep sacks are an amazing product for parents because they eliminate the need to cover your baby with a blanket during the night.

It’s very dangerous to leave blankets in your baby’s crib (and chances are your baby wouldn’t stay under a blanket anyway) as she could suffocate accidentally. Sleep sacks are a very safe solution that gives parents peace of mind and allows babies to sleep comfortably and out of harm's way.

How do you dress a baby under a sleep sack?

How you dress your baby under the sleepsack will depend mainly on the season, the weather, and the temperature of your home and his or her room. It will also depend on the type of sleep sack you’re using. Is it a thin muslin or cotton fabric or is it a thick, padded fleece? All of these factors will ultimately impact your decision.

Obviously, you’ll want to dress your baby cooler in summer and warmer in winter.

One tool that parents can use is the TOG rating, which is a measure of thermal insulation and stands for Thermal Overall Grade. This rating can help you decide how to dress your baby before sleep as the higher the rating, the warmer the fabric. When you're getting your child ready for sleep, check to see if the sleep sack and the clothing have a TOG rating.

As a general rule: a sleep sack with a TOG of 2.5 is best used during cold nights and in the winter, a rating of 1 is ideal for moderate temperatures, and a rating of 0.5 is ideal for summer and hot weather. Fabrics with a TOG rating take the guesswork out of choosing the right clothes for sleeping.

What should my baby wear under a weighted sleep sack?

If your baby is sleeping with a weighted sleep sack, you can follow the same rules as for a regular sleep sack when dressing her.

Choose clothing according to the weather, season, and temperature in your child’s room and, when in doubt, try to dress your baby on the cooler side.

What is the best temperature for a baby to sleep in a sleep sack?

Whether your baby sleeps in a sleep sack or simply in pajamas, you don’t want the room to be too hot or too cold. Use a room thermometer to keep tabs on the temperature and try to keep the nursery or your child’s room around 16 to 20°C or 62 to 68°F.

That being said, you don’t need to obsess over the thermostat. As long as you’re dressed comfortably and feel comfortable with the temperature, your baby probably does too.

Can a baby overheat in a sleep sack?

What should my baby wear under a sleep sack and how do I ensure that she doesn’t get too hot? Overheating in a sleep sack is a valid concern and something about which you need to be aware.

Babies primarily overheat when they’re wearing too many clothes, they have too much bedding, or their bedroom is too hot. If you want to check your baby's temperature, you can:

  •  Look to see if she has red or flushed cheeks, if she's sweating, if she has a fast pulse or if her hair is damp. If you think she’s too hot, remove a layer of clothing and/or move her to another room.
  • Put your hand on your baby’s chest, back, or tummy to see if she’s too hot or too cold. Don’t rely on the temperature of her hands and feet as they tend to be cooler than her core temperature.

Most likely, if your baby's overheating, she will be uncomfortable. She may have trouble sleeping and she could get a heat rash. However, the real danger is that overheating puts your baby at risk for SIDS (Sudden Infant Death Syndrome).

Wearing clothing that is too thick, wearing too many layers, and sleeping in a room that is too warm all increase the risk of SIDS. Remember that babies control their temperature through their heads, so make sure you leave her face and head uncovered to help her avoid overheating.

Can a baby wear pajamas under a sleep sack?

Your baby can absolutely wear pajamas under her sleep sack.

Depending on the time of year and the temperature, you can dress her in light pajamas and a light sleep sack in spring and summer and in a pair of warm, fleece pajamas with a heavier sleep sack in the fall and winter.

What should my baby wear under a sleep sack in the summer?

If you’ve asked yourself, “What do babies wear under a sleep sack in summer?” you might have already imagined it. In the summer your baby should be fine sleeping in a short sleeve cotton onesie, a t-shirt, or even just a diaper under a lightweight sleep sack.

Broadly speaking, you’ll want to choose a sleep sack made from fabrics that breathe and wick away moisture as this will help keep your baby cool.

Of course, whether or not you use air conditioning and the room temperature overall will also help determine the clothes your baby wears. Keep in mind that babies sleep better in cooler temperatures.

What’s most important during the hottest season of the year is to keep your baby cool. Make sure you don’t overdress her in too many layers and if you do layer her, keep them lightweight.

What should my baby wear under a sleep sack in the winter?

When the temperatures drop, you’re going to have to dress your baby warmly at night. If you’re using a sleep sack, you can put your baby in footie pajamas, for example. If the sack is quite thick, choose pajamas that are on the thin side to avoid overheating. Check to see if your sleep sack has a TOG rating and then dress your baby appropriately. 

Now you’re ready to dress your baby for bed

Do babies wear anything under sleep sacks? Now you know that they do! From diapers to onesies to pajamas, you will have to decide what’s best for your baby.

It’s always a good idea to check frequently on her, especially at first, so you can figure out what she is most comfortable wearing. Make sure you monitor her closely and add or remove layers accordingly.

Different seasons inevitably have their adjustment period and it may feel like as soon as you figure out how to keep her cool in summer, winter comes along and you have to transition to a new season. This is par for the course.

A sleep sack is an excellent and safe option for naptime and bedtime that keeps kids cozy and parents at ease. If you were wondering what should babies wear under a sleep sack, you know that it’s a real challenge to appropriately dress your baby according to the time of year and the temperature in her room.

You’ll find that, with practice, you’ll be able to figure out exactly what she needs to wear and how to keep her as comfortable as possible.

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