When to Use a Sleep Sack: A Guide to Starting & Stopping

Happy baby in crib wearing a Woolino 4 Season Ultimate Baby Sleep Bag

Sleep sacks are frequently discussed when parents are selecting sleepwear for their infants. But what exactly are sleep sacks and what are the benefits when using one when compared to more traditional methods like swaddling?

In this article, we’ll find out what a sleep sack is, why they’re beneficial to your little bundles of joy, and when to start – and stop – using them.

Let’s read on to find out more!

What are they?

A sleep sack is similar to a sleeping bag but designed specifically for infants. However, it is snugly fitted around the torso while leaving the neck and head uncovered. The baby's legs are enclosed within a loose fabric bag, creating a warm and cozy environment.

Sleep sacks are widely recognized as a safe and comfortable choice for babies and toddlers, helping to regulate body temperature throughout the night, ensuring a good nights sleep, which is crucial for their growth and development.

Insufficient sleep can weaken their immune system, dampen their mood, and potentially lead to learning difficulties. This is why it's important to ensure that your little one is as comfy as possible, ensuring a good night's sleep.

To achieve this, it is essential to use sleep sacks correctly.

Benefits of Using a Sleep Sack

Not only do sleep sacks provide a comfortable and stylish cocoon for your bundle of joy, but they also provide a number of additional benefits. Let’s take a look at some of the key benefits of a sleep sacks:

  • Safety: Sleep sacks provide a secure sleeping environment for your baby. Unlike blankets, sleep sacks are snugly fitted and do not cover the neck or face, eliminating the risk of strangulation or suffocation. They are considered one of the safest bedding options, as recommended by the American Academy of Pediatricians. Blankets are not recommended until your child is at least 12 months old.

  • Temperature Regulation: Certain sleep sacks, like Woolino's 4-season options, offer the added advantage of regulating your child's body temperature. This reduces the risk of overheating or getting too cold during the night, further enhancing their safety and comfort.

  • Improved Sleep Patterns: Establishing a consistent routine with comfortable and familiar sleepwear can greatly aid your child in falling asleep and staying asleep. Both you and your child will benefit from better-rested mornings and a refreshed start to the day.

  • Reduced Risk of Sudden Infant Death Syndrome (SIDS): Sleep sacks are recognized for their role in minimizing the risk of SIDS. By keeping your baby on their back, the recommended sleeping position, and preventing them from becoming entangled in blankets, sleep sacks contribute to a safer sleep environment. This alone is a compelling reason for many parents to consider using a sleep sack.

  • Convenience for Parents: Sleep sacks are incredibly user-friendly. Unlike other types of fitted nightwear that involve maneuvering small feet into trousers or dealing with cumbersome clothing during diaper changes, sleep sacks offer simplicity. You can easily slip your infant inside, guide their arms in, and fasten the bag around their legs. Some sleep sacks even allow for diaper changes without removing their arms—simply unzip or unfasten the bag, change the diaper, and snugly zip them back in.

Now that we know the benefits of sleep sacks, let’s take a look at when is right to start using a sleep sack and when to stop.

Baby wearing a Woolino 4 Season® Ultimate merino wool Baby Sleep Bag in Whales print

When to Start Using a Sleep Sack

When should you start using a sleep sack? Well, you have the option to use a sleep sack right from birth. However, many parents choose to begin with swaddling and then transition to a sleep sack once their baby starts attempting to roll over. This usually occurs around 3 or 4 months of age, but it can happen earlier. The American Academy of Pediatrics advises discontinuing swaddling as soon as your baby shows signs of attempting to roll over.
Your baby may exhibit certain cues that suggest a dislike for swaddling, such as attempting to kick it off or resisting when you try to put it on. These are clear indications that your baby is ready to graduate to a sleep sack, offering more freedom of movement.
If you prefer, you can transition your baby from a swaddle to a sleep sack earlier. However, it's essential to make the switch once you notice any of these signs. While it may require a bit of effort to make the transition, it is crucial for your baby's safety.

Factors to Consider When Choosing a Sleep Sack

So your baby is ready for a sleep sack, great news! There are a few important factors to consider before deciding what type of sleep sack to buy, and how many you’ll need to buy. Let's take a look at these!

First and foremost, it's crucial to select a sleep sack that fits your baby's age and weight appropriately. While many sleep sacks are designed to accommodate a range of ages, it's essential to keep this in mind. A sleep sack that is too loose poses a suffocation risk, as your child may accidentally slip it over their head. On the other hand, a sleep sack that is too tight can be uncomfortable and restrict your baby's movement and kicking, potentially affecting their hip development and making them more susceptible to hip dysplasia.

At Woolino, we offer a variety of sleep sacks designed for different ages, including options for toddlers and babies aged 2 months to 2 years. To assist you in determining the best size for your little one, refer to the size chart provided below.

Woolino sleep sack sizing chart

Another crucial consideration is temperature regulation. Babies are more like to overheat rather than being too cold, with overheating increasing the risk of SIDS.

Fortunately, Woolino's 4-season sleep sacks are specifically crafted to maintain your baby's optimal temperature throughout the year. Wool has excellent insulation properties, keeping your baby warm in colder weather and effectively releasing heat in warmer conditions. For summer months, we also offer cotton sleep sacks, ensuring your baby stays comfortable.

To help you dress your baby appropriately for different temperatures, we've included a helpful chart below. It will guide you in ensuring your little one remains at a comfortable temperature at all times.

Woolino nursery temperature dressing guide

Additionally, it's important to pay attention to your baby's response to being in a sleep sack. If your baby initially dislikes the sleep sack, you may consider utilizing a one-arm swaddle approach with a swaddle blanket first.

Some sleep sacks can be used in combination with swaddles, as long as your baby doesn't become too hot. This can be a helpful alternative if your baby has difficulty transitioning from a swaddle to a sleep sack.

Different Types of Sleep Sacks

It's important to be aware that there are various types of sleep sacks available, and different ones suit different babies' needs.

For instance, sleeveless sleep sacks are perfect for the summer months. These are the most common type and leave your child's arms free, allowing them to easily roll back onto their backs if they happen to turn over during sleep.

Transitional sleep sacks are another option. They are typically used when transitioning from a swaddle to a sleep sack, as they help bridge the gap between the two. These sleep sacks immobilize the baby's arms while keeping their legs free.

Seasonal sleep sacks are designed to be worn year-round, and Woolino's options, in particular, boast excellent temperature regulation properties. When paired with suitable clothing underneath, these sleep sacks ensure your baby stays warm in the winter and cool in the summer.

Sleep sacks with feet are also worth considering, especially for older children. Woolino offers options suitable for children aged 6 months and up. These sleep sacks allow your child to stand up and walk around while still feeling snug in their wearable bag.

It's also worth thinking about the closures and considering what would be easiest for you as a parent. Some of Woolino's 4-season sleep sacks feature convenient poppers on the shoulders, while their basic baby sleeping bags come with handy zippers. Remember to take into account the type of closure when selecting a sleep sack, as you may find yourself trying to fasten it while half-asleep during a nighttime diaper change.

Baby asleep in crib wearing a Woolino 4 Season® Basic merino wool Sleep Bag in Night Sky print

When to Stop Using a Sleep Sack

Knowing when to stop using a sleep sack is just as important as knowing when to start. Many parents find themselves unsure about when babies should transition from a sleep sack to a blanket.

The American Academy of Pediatrics recommends introducing a blanket after 12 months of age, alongside other loose bedding and looser clothing like proper pajamas, which are considered safe at this stage.

There is no fixed age for discontinuing sleep sacks, but most children naturally transition away from them once they have a blanket on their bed. As your child becomes more mobile, they may find the sleep sack too restrictive and attempt to kick it off or undo the fasteners. This is a clear sign that they are ready for other sleepwear options, such as pajamas or blankets.

However, some children may remain comfortable in a sleep sack for a longer duration, and if they are happy and it still fits well, there's no rush to switch them. As long as they have enough room to kick and move freely, it's safe for them to continue wearing a sleep sack. That's why Woolino offers sleep sacks designed for 2 to 4-year-olds, and even an option for up to 6-year-olds.

When your child displays signs of being ready to transition from a sleep sack, it's time to start dressing them in pajamas and introducing a blanket. Woolino's merino wool blankets make a perfect replacement, providing excellent temperature regulation properties, a cozy feel, and familiarity based on the material used in our sleep sacks.
Initially, your child may prefer to be tucked into the blanket to experience some of the security offered by a sleep sack, while enjoying the freedom of a blanket. It's important to note that some children may not need or show interest in a blanket until they are 2 or even 3 years old, while others may express a desire for one at an earlier age.

Signs that your child may be ready for a blanket include:

  • Cuddling under blankets while reading or watching movies
  • Showing curiosity about your blankets
  • Carrying a blanket to bed with them

Pay attention to your child's cues once they have surpassed 12 months of age, and make the decision based on when you believe they are ready to make the transition.

Alternative Bedtime Attire

You might be wondering how to introduce a blanket to your toddler. One approach is to let them explore and interact with the blanket before bedtime. Encourage them to touch and feel it, allowing them to get a sense of what it's like to lie under it.

When choosing a blanket for your toddler, opt for one that is lightweight and appropriately sized, enabling your child to easily maneuver and handle it. This will promote their comfort and give them the freedom to adjust the blanket according to their body temperature, whether it's pushing it off or pulling it on.

If your child pushes the blanket away during the night, there's no need to fret about putting it back on them. You can check to ensure they are warm enough if you have concerns, but if their body temperature feels appropriate, there's no requirement to cover them with a blanket throughout the night.

That's why having a set of cozy pajamas for your child once they have transitioned from a sleep sack is a wise choice. These pajamas will help them maintain the right temperature. If your child isn't yet comfortable with a blanket and you're concerned about them feeling cold, you can dress them in a couple of layers. As a general rule, your baby should wear one more layer than you find comfortable.

Additionally, cozy socks can keep their feet warm at night, especially as they transition from footed pajamas to footless ones

Baby sucking thumb while holding a Woolino 4 Season® merino wool baby stroller blanket in Stars print

Signing Off

Sleep sacks are an excellent way to keep your baby warm and safe during the night, especially when they are little. There's no definitive answer to how long babies use sleep sacks or when to start using them, as every baby is unique. However, many parents find that sleep sacks are beneficial from a few months old up to 1 or 2 years old. In fact, some babies continue using sleep sacks until they are several years old.

Choosing the right sleepwear for your little one is important, prioritizing their safety and comfort throughout the night. While there are various options available, sleep sacks tend to be the preferred choice for an extended period of their early years. It's worth noting that safety and temperature regulation are the most crucial factors to consider, ensuring that your child sleeps well throughout the night, providing you with better sleep too.

By utilizing sleep sacks, you can have peace of mind knowing that your baby is snug, secure, and protected, promoting a cozy and safe sleep environment. Remember, when it comes to your little one's sleep, prioritizing safety and comfort is key.


How long can a baby wear a sleep sack?

A baby can wear a sleep sack for years if they are safe and comfortable. Because a sleep sack is similar to a sleeping bag, it’s safe for children to use almost indefinitely, as long as it is large enough and they are comfortable.
However, many children start to feel cramped and confined in a sleep sack, and will want to graduate to a blanket and pajamas after 12 months or a couple of years.

Are sleep sacks safe for babies that can roll over?

Yes: because sleep sacks leave the baby’s arms free, they are safe for babies that can roll over. The baby can use their arms to push themselves back onto their backs. This reduces the risk of SIDS and makes your child comfier.

Can babies suffocate in a sleep sack?

Sleep sacks need to be appropriately fitted in order to be safe. If the sleep sack is too large for your child, they may be able to slip down inside it, and this can present a suffocation risk. Always make sure that the sleep sack fits snugly around your baby’s torso, and don’t use sleep sacks that are too large.

Do babies’ arms get cold in sleep sacks?

A baby’s arms can feel cold without the baby being cold; the best way to check whether your little one is warm enough is to touch the skin of their torso or neck. However, if the room is cold, it’s possible for your baby to be cold in a sleep sack. To combat this, you can dress your child in a long-sleeved bodysuit, or put an extra layer on, and keep the room temperature between 68 and 72 degrees F.

Do I need a sleep sack for each season?

Woolino’s 4 season sleep sacks are designed to be used year-round, because they have superb temperature regulation properties. That means you can use one of these throughout the year, rather than needing separate sleep sacks.
However, with other brands, you may need to buy sleep sacks that are appropriate for winter and summer to ensure your child is at the right temperature at all times