What Should My Baby Wear Under a Sleep Sack?

The first thing I bought before my daughter was born was a nice and cozy sleep sack with stars all over it. I have to admit I was a bit lost when it came to how to handle a newborn, but I had seen friends use sleep sacks when I went to visit them and their newborn babies. So I figured it was a must-have item.

When my baby was finally able to wear it, I constantly worried about what she should be wearing under it and, because it was too big, worried she would crawl under it at night. So because of all the worry, I gave it up. By the time I was fine with it, she was already a toddler and determined not to cover herself at night too.

Needless to say, we never used the sleep sack. But when I think of having another child and plan according to what I learned from my first-born, a sleep sack actually takes all worries away. It guarantees your child is covered and does not kick the cover off at night, and makes a nice transition from the swaddle to the blanket.

Most parents (especially new ones), spend their time wondering if their baby is too warm or too cold, going back and forth to their rooms at night to check their temperature (who here relates?!). With experience, many parents have found that the perfect solution to this is layering. By adding or removing layers of clothes, you’ll find it practical to check your child’s temperature and make sure they’re cozy and warm without being too hot. A lot of parents swaddle their newborns for them to be cozy and warm when they sleep. But once your tiny one starts to roll over, a transition to sleep sacks becomes necessary. Sleep sacks are wearable blankets that keep your baby’s arms free but cover their body and feet. For chilly nights, a sleep sack has been found very practical to keep little ones warm and cozy without parents having to worry. But what should a baby wear under a sleep sack? Depending on room temperature and thickness of the sleep sack, what should a baby wear under a sleep sack comes down to long-sleeve onesies (if the room temperature is between 62 and 70 degrees Fahrenheit) or short sleeve onesie (if the temperature is above 70 degrees Fahrenheit), adding PJs on top. Read on for more details!

I know a lot of parents who started using a sleep sack from day one! For my part, it was an anxiety trigger. I found that swaddling during the first few months was much more comforting, giving my baby the coziness she needed. But as she grew, swaddling also became a source of worry (I know, I’m that parent who worries a lot!). So when is swaddling better, and when is a sleep sack better? What is the difference between the two?

Sleep Sack vs. Swaddling

Sleep Sack vs. Swaddling

I know a lot of parents who started using a sleep sack from day one! For my part, it was an anxiety trigger. I found that swaddling during the first few months was much more comforting, giving my baby the coziness she needed. But as she grew, swaddling also became a source of worry (I know, I’m that parent who worries a lot!).

So, you most probably wonder if swaddling better than using a sleep sack, and what is the exact difference between the two. The first and most important difference is that swaddling can only be used during the first few months. Once your baby starts rolling, it can be dangerous and it is time to transition to a sleep sack.

A sleep sack, even though looser than the swaddle, can serve as a positive sleep cue for your baby to have improved and positive sleep habits. Swaddling is more of a way to help babies not startle themselves as they sleep while they still have their Moro reflex. 

So, as we can see, the swaddle and sleep sack are both good for your baby to sleep well. They just serve different stages of development.

What are the benefits of a sleep sack and how do I choose one?

What are the benefits of a sleep sack and how do I choose one?

Basically, a sleep sack can be described as a blanket made like a bodysuit that zips around your baby. It mostly fits babies who are 8 to 9 lbs and more. It has various benefits while you transition to a blanket.

Here is why parents should consider using a sleep sack:

  • A sleep sack is safe and decreases the risk of SIDS. Apart from promoting back sleeping, which is generally recommended, it prevents strangulation or suffocation that can come from being tangled in a blanket.
  • Being that the sleep sack stays on all night, it will keep your baby at a perfect temperature during the whole night. This means your baby will wake up less as there will be no temperature change when they move during sleep. Improved sleep for babies means improved sleep for parents!
  • Some babies start trying to climb out of their crib at a certain age. Being zipped into a sleep sack will decrease the risk of them trying it out and falling out during the night.
  • A sleep sack becomes part of a baby’s sleep ritual and serves as a positive and safe sleep association. It makes their sleep environment safe and familiar, allowing you to even travel and sleep outside the house as their familiar sleep ritual is there with them.

It is very important to make sure your baby’s sleep sack is the right size so they don’t get under it while they sleep. An appropriate sleep sack thickness (0.5 – 1.5 TOG for warm seasons and 3.5 TOG for colder seasons) is also necessary to consider.

If you’re also wondering when to transition from sleep sack to blanket, there is no need to rush. As long as your baby/toddler is happy with it, keep it! You can then see it’s time and switch to a blanket naturally.

So what should my baby wear under a sleep sack?

There are two main rules to know how to keep your baby warm and at a comfortable temperature while they sleep. First, it is normally recommended their room temperature is between 68 and 72 degrees Fahrenheit, and then, do dress them with one additional layer as your own. 

Considering these factors, you can now decide the TOG (or thickness) for your baby’s sleep sack and then what they will wear under it while they sleep. As a general rule, here is how to decide on the thickness:

  • 0.5 TOG for room temperatures above 70°F 
  • 1.0 TOG for room temperatures between 69 and 70°F
  • 2.5 or 3.5 TOG for room temperatures below 68°F 

Once this is sorted, here is what your baby should wear under a sleep sack. Just a note before we move on to that, it is important to know that each baby is different. With time you’ll learn what makes your baby more comfortable.

By checking their neck, you can guess if they are too warm or too cold and remove layers accordingly. So here goes, after knowing the room temperature and the thickness of the sleep sack, your baby should be wearing:

  • If the temperature is high (i.e. above 70 degrees Fahrenheit), your baby won’t need more than his PJs under the sleep sack. Some parents like to add a short-sleeve onesie under it, but it’s up to you. If the temperature is just a bit lower than that, you can add socks.
  • If the temperature is between 62 and 67 degrees Fahrenheit, again depending on the thickness of the sleep sack and room temperature, a long-sleeve onesie and a footed PJ (also depending on the season for its thickness) would keep your baby warm and comfortable.

FAQs

What if my baby rolls in his sleep and he’s wearing a sleep sack?

There is no danger if your baby rolls in his sleep while wearing a sleep sack as long as the sleep sack is the proper size and is properly zipped.

When should I get rid of a sleep sack?

As we mentioned above, there is no age where parents should rush the transition from sleep sack to blanket. Each baby is unique and many toddlers still use their sleep sack. As long as they’re comfortable and it fits, you can use them however long you wish.

Conclusion

It is always difficult to know when your baby is comfortable and whether he is cold or too warm. Knowing the factors that are important to consider, you can easily know what your baby should wear to be comfortable during the night.

A sleep sack is a good option as it has so many benefits. Knowing what your baby should wear under it to have a good night is essential. We hope you found this useful and happy sleep time!

Lynn is a 30-something writer for 1happykiddo and mom of a 4 year-old little girl. When she’s not busy taking care of her daughter or writing, she likes to relax with a book, meditate and connect with loved ones. Oh, and cooking good food too!

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