The TOG rating shows how warmly a sleep sack insulates. As a rough guide, choose 2.5 TOG for a room of 16 to 20 degrees, 1.0 TOG for 20 to 24 degrees and 0.5 TOG for warm nights above 24 degrees. Feel the neck or back to check your baby is pleasantly warm and not sweaty, and keep the cot otherwise empty.
What to remember
- TOG is the insulation value: the higher the number, the warmer the sleep sack.
- Match the TOG to the room temperature, not just the season.
- Feel the warmth at the neck or back, never at the hands or feet.
- Choose a sleeveless sleep sack with a snug neck and arm openings.
What does the TOG rating mean?
TOG is an international measure of how much warmth a fabric holds. On baby sleep sacks you usually see 0.5, 1.0 and 2.5 TOG. A low value is thin and airy for warm nights, a high value is thick and warm for a cooler room.
The TOG replaces loose blankets, which do not belong in a baby's cot according to safe-sleep advice. A well-chosen sleep sack keeps your baby at temperature without anything loose lying in the cot.
Which TOG for which room temperature
A nursery of around 16 to 18 degrees is considered pleasant to sleep in. Use the room temperature as your starting point and adjust the clothing underneath from there. The values below are guidelines, not strict rules.
- 24 degrees and warmer: 0.5 TOG, perhaps just a bodysuit underneath.
- 20 to 24 degrees: 1.0 TOG with a thin bodysuit or pyjamas.
- 16 to 20 degrees: 2.5 TOG with a bodysuit and pyjamas underneath.
- Colder than 16 degrees: 2.5 TOG with an extra warm layer, and check the warmth more often.
Choosing the right size and fit
A sleep sack should fit well around the neck, shoulders and arm openings, so your baby cannot slip down inside it. Choose the size by length and check that the head cannot pass through the neck opening.
Sleep sacks are sleeveless, so your baby can release warmth through the arms. If you want an extra layer, choose clothing under the sleep sack rather than a thicker neck or loose cloths.
How to check your baby is comfortable
Feel the warmth at the neck or between the shoulder blades. If that feels pleasantly warm and dry, it is fine. Cool hands and feet are normal and not a reliable sign of being cold.
A sweaty neck, damp hair or a red, hot colour point to being too warm. In that case choose a lower TOG or leave out a layer of clothing. If you are unsure, talk it over with your health visitor.
Safe use and loose layers
VeiligheidNL advises an empty cot: no blankets, pillows or nests. A well-fitting sleep sack fits that advice exactly, because the warmth is in the sleep sack itself and not in loose items.
Do not let your baby sleep with a hat on and make sure the room does not overheat. A soft blanket is lovely for an awake cuddle or on the go, but does not belong as a loose layer in the bed.
Frequently asked questions
Which TOG do I need for summer?
For warm summer nights above 24 degrees a 0.5 TOG is suitable, perhaps with just a bodysuit underneath. Between 20 and 24 degrees, 1.0 TOG is a comfortable choice.
Can my baby wear clothing under the sleep sack?
Yes. You adjust the warmth with the layer underneath: a thin bodysuit in warm weather, a bodysuit with pyjamas for a cooler room.
How do I know if my baby is too warm?
Feel the neck or back. If it feels sweaty or very hot, or your baby is red and clammy, choose a lower TOG or leave out a layer of clothing.
Sources and review
This guide follows the advice from VeiligheidNL on safe sleep and the information from The Lullaby Trust on room temperature and sleep sacks. Always follow the current safe-sleep advice. Last content review: 17 July 2026.
