Getting baby sleep right is the holy grail of new parenthood. And while no amount of clothing advice will make a newborn sleep through the night, dressing them correctly for bed is one of the most important things you can do for their safety and comfort.
Why Sleepwear Matters
Overheating is a known risk factor for SIDS (sudden infant death syndrome). Babies who are too warm during sleep are at greater risk than babies who are slightly cool. This is why choosing the right sleepwear for the room temperature is not just about comfort — it is about safety.
The Lullaby Trust, the UK's leading safe sleep charity, recommends keeping the room between 16–20°C and dressing your baby in layers appropriate to that temperature.
Sleepwear by Room Temperature
24°C and above: A nappy only, or a nappy with a thin vest. No sleeping bag needed.
22–24°C: A short-sleeved bodysuit with a 0.5 tog sleeping bag.
20–22°C: A short-sleeved bodysuit with a 1 tog sleeping bag.
18–20°C: A long-sleeved bodysuit with a 1–2.5 tog sleeping bag.
16–18°C: A long-sleeved bodysuit with a 2.5 tog sleeping bag.
Below 16°C: A long-sleeved bodysuit, a sleepsuit over the top, and a 2.5 tog sleeping bag.
These are guidelines. Every baby is different, and you should check your baby's temperature by feeling the back of their neck. If it is hot or sweaty, remove a layer. If it is cool, add one.
Sleeping Bags vs Blankets
The Lullaby Trust recommends sleeping bags over blankets for babies. Sleeping bags cannot be kicked off, pulled over the face, or bunched up — all risks associated with loose blankets. They provide a consistent temperature throughout the night without the need for tucking in.
Choose a sleeping bag with a fitted neck and armholes that your baby cannot slip inside. The bag should be the correct size for your baby's weight, not their age.
Fabric Choices for Sleep
Sleep is when fabric choice matters most. Your baby will be in the same clothing for 10–12 hours, unable to tell you if they are uncomfortable. Breathable natural cotton is the best choice — it wicks moisture, regulates temperature, and is gentle against skin that may be pressed into the same position for hours.
Avoid synthetic fabrics for sleepwear. Polyester and nylon trap heat and moisture, increasing the risk of overheating and causing discomfort. Even if the outer sleeping bag is synthetic, the layer against the skin should always be natural cotton.
What to Avoid
Hats indoors — babies lose excess heat through their heads, and a hat during sleep prevents this natural cooling mechanism. Loose clothing with strings, ribbons, or hoods — these are strangulation risks. Thick fleece sleepsuits under sleeping bags — this combination almost always causes overheating.
Keep it simple: a bodysuit, a sleeping bag, and a room thermometer. That is all you need for safe, comfortable sleep.