How do tog ratings affect a baby’s temperature overnight?

What is a tog, and why does the number matter overnight?

The Lullaby Trust’s definition: “Tog is a measure of insulation (warmth) that is used for items like baby sleeping bags and blankets. The higher the number in the tog rating, the warmer the product. In warmer rooms, you should use a lower tog. In cooler rooms, you might use a higher tog.” Tommee Tippee adds the point parents most often miss: “It’s a measure of warmth, rather than thickness.” A thin bag with a dense filling can carry a higher tog than a fluffy one.

Overnight the number matters because the bag is the baby’s only bedding: “If you’re using a baby sleeping bag, don’t add extra blankets on top.” The Lullaby Trust’s reason for caring about warmth is risk, not comfort: “The risk of sudden infant death syndrome (SIDS) is higher in babies who get too hot.” The NHS: “Research shows babies are better to be cooler than too hot.”

The Lullaby Trust on stacking layers: “dressing your baby in two 1.0 tog sleep bags does not make the sleep bag 2.0 tog. This can be dangerous, because air becomes trapped between layers and increases the warmth. Avoid doubling up on layers this way, as it could increase the risk of SIDS.” It adds: “one blanket doubled over counts as two blankets.”

Which tog for which room temperature?

There is no single official chart. The Lullaby Trust says so directly: “Families understandably often look to us for a chart or a more specific guide on matching room temperature to clothing, clothing layers and tog. Unfortunately, we’re unable to provide this specific advice because: every product is made up of different materials… the heat trapped between layers… changes the insulation or warmth of the product significantly… every baby is different.” What it does give is the room range — “The recommended room temperature for babies is 16 – 20°C” — and the instruction to “follow the manufacturer’s tog guide”.

The NHS Best Start in Life page does publish bands, described as those used on commercial bags. Makers publish their own. Side by side they agree on the middle and differ at the edges — including one maker whose support page and product page disagree with each other.

For the question people actually type — a 19°C nursery — every source above lands on 2.5 tog. For a room that sits at 20–21°C the sources split between 2.5 and 1.0, which is where a room thermometer earns its place: The Lullaby Trust says “It can be difficult to guess temperature so use a room thermometer in the rooms where your baby sleeps.”

How should I dress my baby under a 2.5 tog sleeping bag?

Official guidance stays deliberately general here, and this article does not go beyond it. The Lullaby Trust, for 16–20°C: “You may choose to use a baby grow and baby sleep bag.” Cooler than 16°C: “Add an extra layer of clothing or choose a higher tog sleeping bag if your baby feels cold.” Warmer than 20°C: “it’s fine to have your baby in a lightweight layer such as a short sleeve bodysuit, or even just a nappy.”

The NHS, for winter nights: “A sleepsuit and either a sleeping bag (check the manufacturer’s recommendation for winter tog thickness) or a sheet and/or blanket should be fine. If you’re using a sleeping bag and feel like your baby is cold, add an extra layer of clothing – but not extra blankets.” For summer nights: “A vest or just a nappy is fine on the warmest nights.”

Two things both bodies rule out regardless of tog: hats indoors (“Babies lose heat through their heads, so if their heads are covered, the baby can overheat”) and weighted bedding (“Weighted swaddles, blankets and sleeping bags are not recommended for babies under one year as there is a risk of overheating and head covering”).

How can I tell if my baby is overheating in a sleep sack?

Both the NHS and The Lullaby Trust give the same physical check, and it is the only one either of them uses. The Lullaby Trust: “To do this, feel your baby’s chest or the back of their neck (your baby’s hands and feet will usually be cooler, which is normal). If your baby’s skin is hot or sweaty, it means they are too hot so remove one or more layers of bedclothes or bedding.” The NHS: “Check your baby’s temperature by feeling their chest or the back of their neck. Do not worry if their hands or feet feel cool, this is normal.”

1. 1
   Feel the chest or the back of the neck Not the hands or feet. The Lullaby Trust and the NHS both say cooler extremities are normal and are not a reason to add layers.
2. 2
   Hot or sweaty means too hot The Lullaby Trust’s instruction is to “remove one or more layers of bedclothes or bedding”. With a sleeping bag that means a lighter tog or fewer clothes underneath, not opening the bag.
3. 3
   Cold chest means too cold “If your baby feels cold, add an extra layer of clothing or choose a higher tog sleeping bag.” Not a blanket on top, and not a hat.
4. 4
   Read the room thermometer If the room is outside 16–20°C, The Lullaby Trust’s advice is to change the layers or the bag; in hot weather, lighter bedding, a fan not aimed at the baby, and an open door and window where that can be done safely.
5. 5
   If the baby seems unwell The Lullaby Trust: “If your baby has a fever or you are worried about them, you should call your GP or 111.” The NHS lists when to call 999. This guide does not add to that.

Why does my baby wake sweaty in a 2.5 tog sleeping bag?

Working only from the sources above, a sweaty baby in a 2.5 tog bag points at a short list of causes, all checkable in a minute.

• The room is warmer than the bag’s band. 2.5 tog is a 16–20°C bag on every published chart. A room that reads 21°C at 3 a.m. — common with the heating timer, or in a flat — has moved into the 1.0 tog band. The Lullaby Trust: use “a room thermometer in the rooms where your baby sleeps as it can be hard to gauge temperature”.
• Too many layers underneath. A vest, a sleepsuit and a cardigan under a 2.5 tog bag is more than any chart shows for 16–20°C. The Lullaby Trust’s baseline for that band is “a baby grow and baby sleep bag”.
• Something added on top. A blanket over a sleeping bag is the one combination The Lullaby Trust and Tommee Tippee both warn against outright: “Do not use a Grobag in combination with other bedding items e.g., a cot duvet or blanket.”
• A hat, or a hood. Both bodies say to remove hats indoors; EN 16781 does not permit a hood on a sleeping bag at all.
• The cot is next to a heat source. The Lullaby Trust: “Ensure your baby’s cot or Moses basket isn’t placed near a heat source, such as a radiator, heater or in direct sunlight.” The NHS: babies should “never sleep next to a radiator, heater or fire”.
• The baby is unwell. The Lullaby Trust: “When babies feel unwell with a cold or high temperature (fever), they may be warmer than usual. Your baby should be dressed for their environment – it’s important not to feel tempted to wrap an unwell baby up more than usual.” If in doubt, its instruction is to call your GP or 111.

If the thermometer, the layers, the bedding and the cot position all check out and the baby is still hot and sweaty, the remaining variable in the Lullaby Trust’s list is the baby: “Every baby is different, so our room temperature guidance is intended to be used as a guide.” Dropping to a 1.0 tog bag in a 19°C room is not against any published guidance, provided the chest check says the baby is not then too cold.

Should I choose a 0.5 tog or 1 tog bag for summer?

British summer nights rarely hold one temperature, so the honest answer from the charts is: read the thermometer at bedtime, not the forecast. Tommee Tippee: “Always consider the room temperature when selecting your child’s sleepwear, rather than the outdoor temperature.” At 20–24°C every source above says 1.0 tog. At 24°C and above the NHS and Snuz say 0.5 tog; Tommee Tippee sells 0.2 tog for that band and M&S puts 0.5 tog at 25°C and above.

In a heatwave The Lullaby Trust stops talking about togs: “In really hot weather, it’s fine to have your baby in a short sleeve vest or even just a nappy.” Its hot-room list is lighter bedding and clothing, an open door and window where that can be done safely, a fan not aimed at the baby, and curtains closed by day.

In shortTog is a warmth number, and the only official room range is 16–20°C. In that range every published chart says 2.5 tog; above it, 1.0 then 0.5 or 0.2. The Lullaby Trust will not publish a chart because products and babies differ — so use the chart for the bag you own, keep a thermometer in the room, and let the chest and back-of-neck check, not the number on the label, decide whether tonight’s bag is right.