Will a Sleep Sack Help My Baby Sleep Through the Night?

Some parents say sleep sacks are the key to helping infants get better sleep. Here’s what a sleep sack is, and when to stop using one.

Mixed race baby girl sleeping on bed
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There are a lot of questions when it comes to helping your baby sleep. This is particularly true if your baby struggles or isn’t an easy sleeper. The internet is rife with items, gadgets, and methods designed to help your baby sleep better so everyone can get a better night’s sleep. One of those is sleep sacks. Do they work and will one help your baby sleep?

What is a sleep sack?

Sleep sacks are basically what they sound like — a wearable blanket that you zip or snap a baby into. Sleep sacks are worn over pajamas, onesies, or clothing, and cover the torso and legs without creating lose fabric that can be a suffocation hazard.

The American Academy of Pediatrics' (AAP) safe sleep guidelines recommend not placing loose items in a crib with a baby during sleep. This includes soft blankets, pillows, stuffed animals, or other objects. Sleep sacks, which are similar to a sleeping bag that babies wear to sleep, are typically used after a baby outgrows swaddling as a way to keep a baby warm before he or she is old enough to sleep in jammies with a blanket.

Made of soft, blanket-like material, these garments typically have open arms that leave baby’s arms free, though can come with sleeves for cooler seasons, if desired.

Do sleep sacks work?

For a parent navigating a market packed with baby gadgets and items of apparel all claiming to help with better sleep, sleep sacks can seem like just another item, leaving them wondering if sleep sacks really work. Natalie Barnett, Ph.D., Vice President of Clinical Research at Nanit, states, “Sleep sacks work very well! They are a great way to keep a baby covered and cozy while allowing them the freedom of movement in their crib space.”

Since sleep sacks aren’t meant to constrict movement like a swaddle or some of the sleep suits babies wear, a sleep sack won’t fix all of your sleep troubles. So, if your baby has trouble sleeping, a sleep sack probably won’t do much to solve them, but it could make your baby more comfortable, which could potentially improve sleep, especially when used regularly as a set sleep routine.

Be sure your baby is safe in a sleep sack

Newborn babies are safest in a swaddle. A swaddle — lovingly referred to as a baby burrito — minimizes their startle reflex and keeps them warm and contained. But once a baby is old enough to roll from their back — the safest sleep position — onto their stomachs (usually around two months), a swaddle is no longer safe. Sleep sacks then become a good option for babies who can no longer be swaddled.

Sleep sacks need to fit properly to be safe for your baby. Sleep sacks come in different sizes. Be sure to use the correct size for your baby or toddler, by their length and age. The incorrect size could be dangerous. “A sleep sack should fit your baby well and not be too big or too small.” Barnett says. “If it is too big, it can ride up and cover your baby's face, which can be a suffocation hazard. If it's too small, it may not have enough room for your baby to freely move their body or legs, which is important for them to do once they are starting to move.”

Sizes may vary based on style or brand but the style with the closed bottom usually fits up to 24 months, 36 pounds, or 40 inches. After this size, sleep sacks are available in toddler sizes, 2T-5T. Toddler sleep sacks modify the design, with leg holes at the bottom that allow your little one to have their feet out so they can stand easily without falling, but with a sack connection between the two sides to keep them from raising their leg high enough to climb out of their crib.

An additional consideration is the material of the sleep sack. “Make sure you get a sleeping [sack] made of a breathable fabric like cotton, for example, so your baby will not overheat in it,” Barnett advises. Overly warm room temperatures or pajamas increase a baby’s risk of sudden infant death syndrome (SIDS), so it’s important to consider the breathability of the fabric and any other ways the baby could overheat. “Look at the Thermal Overall Grade (TOG) rating to determine your room's proper temperature when using a sleep sack.” The TOG is a scale used for baby dressing based on the room temperature, on a scale from .5 to 3.5. The lower the TOG, the lighter the fabric, so a room temperature of approximately 72-75°F would mean a .5 TOG, with a light cotton or muslin sack, while a cooler room temperature, such as 61-68°F, mean a higher TOG of 2.5-3.5, sometimes made of fleece or more insulated fabric. Babies do not need to be heavily dressed and often don’t need layers.

When you need to stop using a sleep sack

Sleep sack sizes grow with your little one through much of their toddler time. Your little one can stay in a sleep sack until they can stand and then they can move to one where their feet are out. There are a lot of options, so you don’t have to transition out until you and your baby are ready unless there is a safety risk. Just be sure the sleep sack you’re using fits properly.

Another time that many parents stop using sleep sacks is when a child learns how to unzip or remove the sleep sack, as they could climb out or hurt themselves in the loosened garment. Some parents have gotten creative and turned the sleep sack backward, putting the zipper in the back, to keep it on a bit longer. This might be helpful for those little ones who try to climb out of their crib, remove their diapers, or other sneaky things when parents aren’t looking. Otherwise, it may be time to let the sleep sack go.

How to transition out of a sleep sack

You may not need to transition from a sleep sack. Sleep sacks give your baby enough freedom to move their legs that they may not notice it’s gone. Some babies, on the other hand, may not like being without it. This can be a personal transition.

You can move away from the sleep sack when your baby is big enough to sleep with a small blanket, which according to the AAP, is age 1. “You will likely stop using a sleep sack when your baby moves out of the crib and they can get in and out of bed themselves, which can be a little harder with a sleep sack on,” says Barnett. When they move into a toddler bed, you need to let the sleep sack go too. Sleep sacks are not safe to walk, crawl, or climb in.

When you shouldn’t use a sleep sack

Barnett advises not using a sleep sack if your baby’s room is too warm.

It’s also not a good idea to use a sleep sack if your baby is already wearing heavy pajamas, as the baby could overheat, even in a temperature-controlled room.

It’s also not a good idea to use a sleep sack on your baby if the sack isn’t properly sized, or if the baby is able to remove it on their own.

Is it ok to use a weighted sleep sack?

It is important to not use a weighted sleep sack. It isn’t safe to use any weighted item with your baby, ever. The AAP states urges parents to avoid weighted sleep sacks or any other weighted item during sleep — blanket, sleepers, swaddles, etc. — increases the risk of SIDS and should not be placed on or near a baby.

Sleep sacks are a safe alternative to blankets and loose bedding, which can be dangerous to infants during sleep. The AAP recommends using sleep sacks that properly fit and don’t cause overheating of infants and toddlers. While these handy items don’t promise sleep miracles, they can provide the benefit of keeping your little one comfortable and potentially keep them from climbing while in their crib.