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The baby sleeping on a white sleep sack

What Should My Baby Wear Under a Sleep Sack?


Sleep sacks are a blessing for parents, keeping little ones snug and secure throughout the night.

But what should your little one wear underneath?

Overdressing leads to overheating, while underdressing leaves your baby chilly and uncomfortable.

Understanding TOG Values

It stands for “Thermal Overall Grade” and measures the warmth of a sleep sack. The higher the TOG, the warmer the sack. Here’s a general guideline:

  • 0.5 TOG: Ideal for hot summer nights or rooms with temperatures above 75°F (24°C).
  • 1.0 TOG: Perfect for warm weather or rooms between 68°F and 75°F (20°C and 24°C).
  • 2.0 TOG: Suitable for cooler weather or rooms between 61°F and 68°F (16°C and 20°C).
  • 3.0 TOG: Best for cold winter nights or rooms below 61°F (16°C).

Choosing the Right Clothes for Underneath

Now, let’s explore the clothing options that pair perfectly with different tog ratings and seasons:

Warm Weather (0.5 – 1.0 tog)

  • Keep it cool and breathable: Opt for natural fabrics like cotton or bamboo. Short-sleeved onesies, thin muslin blankets, or lightweight pajamas are ideal.
  • Diaper-only is okay: In very hot weather, just a diaper under a 0.5 tog sleep sack might be enough. Monitor your baby’s temperature to ensure they’re comfortable.

Temperate Weather (1.0 – 2.0 tog)

  • Layer up wisely: Long-sleeved onesies, thin cotton pajamas, or footed pajamas are fantastic choices. Remember, avoid heavy fabrics or multiple layers to prevent overheating.
  • Consider the room temperature: Adjust the clothing based on whether your baby sleeps in a warm or cool room.

Cold Weather (2.0 – 3.0 tog)

  • Fleece it up: Fleece or flannel pajamas offer extra warmth. Double-layered cotton sleep sacks are also great options.
  • Cozy toes matter: Footed pajamas keep little feet warm, especially in colder rooms.

Tips for Safe and Cozy Sleep:

Check the neck

Your baby’s neck should feel cool, not clammy. If it’s sweaty, they’re probably overdressed.

Feel the hands and feet

Cool hands and feet are okay, but if they’re cold, add a layer.

Use a room thermometer

Aim for a room temperature between 68°F and 72°F for optimal sleep.

Avoid layering under thin sacks

Overdressing under a lightweight sleep sack can raise the tog rating too high, causing overheating.

Choose natural fabrics

Opt for breathable materials like cotton, bamboo, or wool to avoid trapping heat and moisture.

Skip the extras

Hats, socks, and other accessories under a sleep sack are unnecessary and can increase the risk of overheating.


With these tips and a little trial and error, you’ll find the perfect combination of sleep sack and clothing to keep your baby comfortable and safe all night long.

Remember, the goal is to create a cozy sleep environment that allows your little one to drift off to dreamland peacefully.

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Sara Abdalla

Sara Abdalla

Sarah holds a Bachelor's degree in Child Development and her work has been featured in reputable parenting magazines, online forums, and advisory boards.

But Sarah doesn't just stop at research and expertise. As a mother of two herself, Sarah has amassed a wealth of experiences about what truly works for babies and what falls short of expectations.