When Do You Need a Winter Sleep Sack For Your Baby?

Bedtime is all about creating a comfortable atmosphere that makes your little bub feel safe, warm, and loved. The right room temperature and a cozy winter sleep sack can help your little one relax and slip into a peaceful slumber. Putting a baby into a winter sleep sack also acts as a sensory cue for sleep—potentially making the evening bedtime ritual smoother for everyone.

Winter sleepwear, such as a 3.5 TOG sleep sack, keep babies and toddlers warm in their cribs even through the coldest months. When the weather becomes chilly, it’s time to upgrade to a warm winter sleep sack for your little one.

Are sleep sacks warm enough for winter?

Not every sleep sack is winter-appropriate. Just as you may add layers to your bedding to stay snug and cozy in the cold season, you want to consider the warmth your baby’s sleepwear provides and whether they need to upgrade to a winter sleep bag or sack.

To determine if your current sleep sack is warm enough for winter, you must consider three main factors:

1. Your baby’s room temperature
2. Any bedtime layers under the sleep bag—such long sleeve PJs or short sleeve PJs
3. Your baby’s typical temperature (do they usually run a little warm or cool?)

A sleep sack is warm enough for winter if the room temperature is reasonable and your little one wears long sleeves or a footed sleeper. Homes that raise the thermostat in the winter create warmer rooms and nurseries, which must be accounted for when getting your little one ready for bedtime. A winter sleep sack aims to keep your little love at just the right temperature—neither too hot nor cold.

Different temperature ranges in a room correspond with a TOG rating for a sleep sack. This number helps you determine which sleep sack is the right fit for your home environment.

What TOG rating is best for a winter sleep sack?

Thermal Overall Grade (TOG) measures how much heat the fabric retains. The warmest sleep sacks have the highest TOG rating. There isn’t a single TOG rating that is best for a winter sleep sack, as the TOG your baby needs depends on the temperature of their room.

To measure the temperature in the room, use a combination of a thermometer and the thermostat for an accurate number. This temperature informs the TOG you need for a winter sleep sack. 

0.25 TOG sleep sacks:27°C+ (81°F+)0.5 TOG sleep sacks:24–27°C (75–81°F)0.6 TOG sleep sacks:23-27°C (75-81°F) 1.0 TOG sleep sacks:20–24°C (68–75°F)2.5 TOG sleep sacks:16–20°C (61–68°F)3.5 TOG sleep sacks:10–16°C (50°F–61°F)4.0 TOG footed sleep sacks:8–14°C (46.4°F–57.2°F)

3.5 TOG winter sleep sacks and 4.0 sleep bags are quite popular for those who live in the chilliest climates, as they enable you to save money on heating while ensuring your baby is comfortable and cozy throughout the coldest winter nights.

What is the warmest sleep sack available?

Sleep sacks with a 4.0 TOG rating are the warmest on the market—though very few baby clothing companies make sleepwear with this rating. A 4.0 TOG winter sleep sack is meant for colder temperatures, where the room temperature is below 16 degrees Celsius. 

Nest Designs is one of the only baby clothing companies to offer a 4.0 TOG footed sleep bag. In addition to providing warmth in cold settings, we make our winter sleep bags with high-quality, eco-friendly materials.

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

The rule of thumb for baby sleeping temperatures is not too hot or cold. The ideal winter temperature range for babies to sleep is between 20–22 Celsius (68–72 Fahrenheit). Layering long-sleeve PJs under a sleep sack in a colder room adds extra warmth.  

Do babies sleep better in the cold?

Finding the temperature sweet spot helps your little love snooze soundly.

Your baby’s internal body temperature is linked to their sleep patterns. Early in the morning, your little bub’s body temperature rises in preparation for waking up. If they become too warm in the middle of the night, it can cause them to stir and open their eyes before falling back asleep...or it may cause them to rise and shine earlier than you would like.

Conversely, right around bedtime your baby’s body temperature drops as melatonin levels increase. With this in mind, you could say that babies sleep somewhat better in the cold. 

How do I know if my baby is cold at night?

Certain parts of the body are tell-tale indicators for whether your baby is cold. You can check their arms, legs, tummy and cheeks, as these areas will feel cool if your little cutie is cold.

Frequent waking can also mean that your baby is cold, so if this is the case, you may want to upgrade to a winter sleep sack with a higher TOG rating or layer warmer PJs under their sleepwear.

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

The best solution for sleepwear inside a sleep sack during the winter is a bodysuit, such as a onesie or sleeper. These cute and cozy outfits provide full coverage without being too hot and can be purchased in various thicknesses and lengths to cover a variety of seasonal temperature scenarios. Short-sleeved onesies work well during spring and summer, while long-sleeved sleepers are great for the winter. 

Do I need a winter sleep sack?

In short, yes. A winter sleep sack moves with even the most active sleepers, keeping them comfy throughout the night and preventing the blanket from falling off during sleep. In contrast, according to the Canadian Pediatric Society, blankets or quilts are a safety concern and should not be used for babies under one year old. 

Are blankets warmer than sleep sacks?

Experts at the American Academy of Pediatrics recommend not using regular blankets for babies under one. So, any temperature differential is irrelevant because sleep sacks easily enable a baby to be comfortable—a key factor contributing to good sleep.

For little ones over a year, parents can offer them warmth with a toddler blanket. These work best for sound sleepers who don’t move around too much at night (as they’re less likely to kick off the blanket). Nest Designs has various TOG rating blankets that help your little love feel snug as a bug.

Overall, a well-fitted sleep sack plus the right PJs for the season are a better solution for your baby’s sleep needs. 

Snug and Comfy Down to Their Tiny Toes 

The best winter sleep sacks are not only cute but safe and help your baby sleep soundly. There’s no need to reach for blankets or quilts when sleep sacks do such a great job of moving with your baby, keeping them wrapped in comfort throughout their nap or nighttime sleep.

For cozy, comfy sleep sacks with various TOG ratings and premium materials, check out our Nest Designs sleep bags and sleep suits. For babies that need extra warmth, tuck them into bed wearing 3.5 TOG sleepwear or 4.0 TOG sleepwear.