Quick answer

Pick the sleep sack TOG by your nursery's actual temperature, not the calendar. As a working rule: around 24–27°C use a 0.5 TOG, around 21–23°C use a 1.0 TOG, and around 16–20°C use a 2.5 TOG. Start with what your baby wears underneath, then adjust the TOG to the room — and always use a sleep sack instead of a loose blanket for safer warmth.

What TOG actually measures (and what it doesn't)

TOG stands for Thermal Overall Grade, a lab measure of how much heat a garment traps. Higher TOG means more insulation, not a higher temperature setting. It says nothing about fit, fabric breathability, or how your baby's own body heat behaves — which is why two babies in the same room can need different TOG ratings.

This is also why there is no universal 'winter TOG' or 'summer TOG.' A 2.5 TOG sack in an overheated 24°C room can be riskier than a 1.0 TOG sack in a cool 19°C room. Treat TOG as one variable in a system that includes room temperature, base layer, and your baby's sleep habits.

Build a simple temperature-to-TOG chart for your nursery

Before you buy anything, put a thermometer at mattress level in the nursery and check it for a few nights. Crib height runs a degree or two cooler than adult head height, so a wall thermostat can mislead you. Once you know the overnight range, match it:

Use this as a starting point, then adjust based on how your baby feels at the back of the neck and chest — not the hands and feet, which normally run cooler. If the chest is hot or damp, drop a TOG or lighten the base layer. If the chest is cool and the baby is fussy, step up.

  • 0.5 TOG: roughly 24–27°C, over a short-sleeve bodysuit or light pajamas
  • 1.0 TOG: roughly 21–23°C, over a bodysuit or light two-piece set
  • 2.5 TOG: roughly 16–20°C, over long-sleeve pajamas or a bodysuit plus pajamas
  • Below 16°C: warm the room rather than stacking TOG ratings; very high TOG sacks are not a substitute for heating

Layer underneath before you change the TOG

The most common mistake is jumping from a 1.0 TOG to a 2.5 TOG the moment the season changes, while leaving the base layer unchanged. Seasonal baby sleepwear layering works from the skin out: start with a breathable bodysuit or pajama set, then choose the TOG that fills the gap to your room temperature.

A cotton or CloudBlend two-piece set under a 1.0 TOG sack covers a wide shoulder season range, and you can swap to a warmer sack or add a bodysuit as nights cool. This gives you more control than owning one very warm sack and one very light one.

Sleep sack vs blanket warmth: why the sack wins

A sleep sack is a wearable blanket, so it stays on through rolling, kicking, and standing up in the crib. A loose blanket can be kicked off — leaving a cold baby — or pulled over the face, which is why safe sleep guidance favors wearable options for infants.

On warmth, a 1.0 TOG sleep sack over pajamas generally matches a light blanket plus pajamas, but without the re-covering cycle at 3 a.m. The tradeoff is that a sleep sack's warmth is fixed: you cannot add a layer mid-night without waking your baby, so choosing the right TOG up front matters more.

Your 5-step TOG selection process

  1. Measure the nursery overnight: Place a thermometer at mattress level and record the low and high for three nights. Use the coolest hour, usually 3–5 a.m., as your reference point. Checkpoint: if your range spans more than 3°C, plan two TOG options rather than one.
  2. Choose the base layer first: Pick a bodysuit or pajama set appropriate to the season — short sleeve for warm rooms, long sleeve for cool ones — before touching the TOG rating. Common mistake: choosing the sack first, then realizing the pajamas underneath make the baby too hot.
  3. Match TOG to the coolest hour: Use 0.5 TOG around 24–27°C, 1.0 TOG around 21–23°C, and 2.5 TOG around 16–20°C. Round toward the cooler rating if your baby runs warm. Checkpoint: the back of the neck should feel warm and dry, not hot or damp.
  4. Test for two nights before changing anything: Change only one variable at a time — the TOG or the base layer, not both. Note wake-ups and how the chest feels in the morning. Common mistake: swapping sack and pajamas on the same night, which makes it impossible to know what worked.
  5. Size for fit, not for growth: A sack that is too long can bunch around the face when your baby stands; one that is too tight restricts leg movement. Follow the size option that matches your baby's current height and weight. Next step: recheck fit and TOG at every growth spurt and at each seasonal change.

Products that fit this method

  • Cormorant - CloudBlend™ Sleep Sack TOG 1: Cormorant - CloudBlendTM Sleep Sack TOG 1, a wearable blanket in CloudBlendTM fabric with a warm earthy brown colorway. A 1.0 TOG sack is the workhorse for rooms around 21–23°C, which covers most heated nurseries and shoulder-season nights.
  • Kitty - CloudBlend™ Sleep Sack TOG 1: Kitty - CloudBlendTM Sleep Sack TOG 1, same CloudBlendTM fabric and 1.0 TOG rating. If you already know 1.0 TOG is your baby's range, the second colorway lets you keep one in the wash and one in the crib without changing the warmth.
  • Cherry - CloudBlend™ Short Sleeve Pajamas Set: Cherry - CloudBlendTM Short Sleeve Pajamas Set, a two-piece short-sleeve set in CloudBlendTM fabric. Short-sleeve pajamas are the right base layer under a 1.0 TOG sack in warmer months, so you can keep the same sack and lighten the layer instead of buying a new TOG.