Baby Sleep Sack TOG Guide: How Warm Is Too Warm?

The right pajamas are something many parents wrestle with, especially at night. Clothing that's too warm is as much a problem as clothing that's too cool, and since your baby can't correct for it while asleep, you settle the question when you reach into the drawer.

Why the Right Pajamas and Sleep Sack Matter

During sleep, your baby can't yet regulate their body temperature. Pajamas that are too thick lead to heat buildup and restless sleep; clothing that's too thin lets your baby get cold. Which sleepwear fits comes down to two things: the room temperature and the sleep sack (called a sleeping bag in the UK and Australia).

The Optimal Room Temperature

The recommended bedroom temperature is 16 to 18 °C (61 to 64 °F), the same range the recommendations for a safe sleep environment set out. That often feels chilly to adults, but it's the safe range for your baby, provided the clothing matches it.

Sleep Sack TOG Ratings by Room Temperature

The TOG value describes the thermal resistance of textiles: the higher the value, the warmer the sleep sack. Low ratings belong in warm rooms, higher ones in cool rooms. Which rating suits which room temperature:

• 0.5 and 1.0 TOG: warm rooms from 20 to 27 °C (68 to 81 °F), the range for summer nights and well-heated rooms
• 1.5 TOG: 18 to 24 °C (64 to 75 °F), the in-between range for spring and fall
• 2.0 TOG: 16 to 22 °C (61 to 72 °F), which covers the recommended bedroom range well
• 2.5 TOG: 15 to 20 °C (59 to 68 °F), for cooler nights
• 3.0 and 3.5 TOG: only for very cool rooms of 15 to 17 °C (59 to 63 °F)

Two sleep sacks usually cover you at the start: a light one for warm nights and a warmer one for the rest of the year. Sleep sacks sold in the US often carry no TOG rating; as a rough guide, a light muslin or cotton sleep sack is about 0.5 TOG and a warm quilted winter one 2.5 TOG.

What goes underneath follows the TOG value: the warmer the sleep sack, the fewer layers below it. At 16 to 17 °C (61 to 63 °F) with a 2.5 TOG sleep sack, a long-sleeve cotton bodysuit (onesie), thin pajamas, and thin socks work well. At 25 to 27 °C (77 to 81 °F), a short-sleeve bodysuit in a thin 0.5 or 1.0 TOG sleep sack is enough.

Dressing at Night: Less Is More

The urge to bundle your baby up “extra warm” quickly leads to overheating. Breathable fabrics in several thin layers are the better choice and also prevent moisture buildup. A typical setup at around 18 °C (64 °F) is a long-sleeve cotton bodysuit, thin pajamas, and a sleep sack with 2.0 TOG. Go with a 2.5 TOG sleep sack instead and a short-sleeve bodysuit underneath is enough.

Checking your baby's neck tells you whether the combination works: place two fingers on the back of your baby's neck. It should feel warm and dry, not sweaty. Cold hands or feet, by contrast, are normal for babies and no sign that they're cold.

Pajamas and Sleep Sacks for Every Season

In summer, a short-sleeve bodysuit with a thin 0.5 or 1.0 TOG sleep sack. In spring and fall, a long-sleeve bodysuit, thin pajamas, and 1.5 to 2.0 TOG. In winter the room still sits at 16 to 18 °C (61 to 64 °F). Pair it with a long-sleeve bodysuit, warm pajamas in terry or wool-silk, and a 2.0 or 2.5 TOG sleep sack. Only when the room drops to 15 to 17 °C (59 to 63 °F) do 3.0 or 3.5 TOG come into play, and then with less underneath.

Make sure the pajamas have no irritating seams, buttons, or elastic cuffs, fit comfortably, and are ideally made of natural materials like cotton or wool.

The Weather Matters at Night Too

Outdoor temperature affects indoor temperature, especially in older buildings or without air conditioning. A thermometer in the bedroom takes the guesswork out of it and tells you which sleep sack is right tonight. The Wetterbaby app takes not only the daytime weather but also the nighttime temperature into account and recommends day by day what your baby should wear at night.

Source:
AOK health magazine, Sudden infant death (SIDS): how parents can prevent it (in German)