Sleep sacks and TOG ratings: how to choose and use a baby sleeping bag
A wearable blanket keeps your baby warm without loose bedding. Choosing one comes down to three things: the right tog for your room, a snug fit, and no extras.
Updated October 13, 2026 · sources checked October 13, 2026
In short
TOG measures how warm a fabric is: the higher the number, the warmer the sleep sack. Aim for a room at 16 to 20°C, then follow the maker's TOG guide for that temperature, because the Lullaby Trust says no single chart fits every product. Choose the size by weight, a snug neck and armholes, no hood, never weighted, and no blanket on top.
Why a sleep sack
Loose blankets are one of the things the AAP asks parents to keep out of the crib, because they can cover a baby's face. The AAP says infant sleep clothing, such as layers or a wearable blanket (sleep sack), is preferred over blankets to keep a baby warm. The Lullaby Trust adds that a sleep bag stops a baby wriggling down under covers and getting their head covered.
What TOG means
TOG is a measure of insulation used for baby sleeping bags and blankets. The higher the number, the warmer the product: lower TOG for warmer rooms, higher TOG for cooler rooms (Lullaby Trust).
Why we do not print a "TOG chart". The Lullaby Trust explains that it cannot give a chart matching room temperature to clothing and tog, because every product uses different materials, layers trap different amounts of heat, and every baby is different. Charts you see online come from manufacturers for their own products. Use the one supplied with your sleep sack.
Match the sack to the room, not the season
Start with the room. The recommended temperature for a baby's room is 16 to 20°C, measured with a room thermometer (Lullaby Trust); the AAP's family site gives 68 to 72°F for infants and children. Then adjust:
| Room temperature | What the Lullaby Trust suggests |
|---|---|
| Below 16°C | Do not add blankets on top of a sleep bag. Add a layer of clothing, or use a higher tog sleep bag. |
| 16 to 20°C | A lightweight, well-fitting sleep bag over a baby grow, or light bedding firmly tucked in. |
| Above 20°C or hot weather | A light layer such as a short-sleeve bodysuit, or just a nappy, is fine. |
Whatever the number, check your baby: feel the chest or the back of the neck. Hot or sweaty means too warm, so remove a layer. A cold chest means add a layer or a higher tog. Cool hands and feet are normal.
Three mistakes that make a baby too warm
- Layering two sleep bags. Two 1.0 tog bags do not make 2.0 tog: air trapped between layers adds warmth (Lullaby Trust).
- A blanket doubled over. It counts as two blankets.
- A hat or hood indoors. Babies release heat through the head; the Lullaby Trust and AAP both say no hat indoors.
What to check before you buy
Characteristics, not brands:
| Feature | What to look for | Why |
|---|---|---|
| Size | Chosen by your baby's weight, following the maker's guide | The Lullaby Trust notes most sleep bags are fitted by weight, not age |
| Neck and armholes | Well fitted around the neck and shoulders | So your baby cannot slip down inside |
| Hood | None | Head covering can cause overheating |
| Weight | Not weighted | Weighted sleep bags are not recommended under one year (Lullaby Trust, AAP) |
| TOG label | Clearly stated, with the maker's room-temperature guide | So you can match it to your room |
| Arms | Sleeveless or free arms once your baby rolls | Sacks that compress arms and chest must stop at rolling (AAP) |
| Standard | In the UK, BS EN 16781:2018 for sleepbags | The Lullaby Trust recommends buying to the relevant British Standard |
| Second-hand | Check recalls first | The Lullaby Trust lists recent recalls of sleeping bags |
The Lullaby Trust also reminds parents that a safety standard checks general safety (not falling apart, fire), not SIDS risk, and that it does not recommend individual brands.
Sleep sack or swaddle?
A swaddle wraps the arms; a sleep sack leaves them free. The AAP says swaddles and sleep sacks that compress the arms, chest and body should stop once a baby shows signs of starting to roll, while sleep sacks that let your baby move freely can be used as long as you want. Many families move from a swaddle to an arms-free sleep sack at that point.
The rest of the safe sleep rules still apply
A sleep sack is not a safety device on its own. Your baby still sleeps on their back, on a firm flat mattress, in a bare crib in your room: see the full safe sleep checklist. If your baby has a fever, do not wrap them up more than usual; the Lullaby Trust advises calling your GP or NHS 111 in the UK, or your pediatrician in the US, if you are worried.
Building your list? Sleep sacks sit alongside the few true essentials in our baby registry checklist.
Questions parents ask
What tog sleep sack for 18°C?
18°C sits inside the recommended 16-20°C range, where the Lullaby Trust says a lightweight, well-fitting sleep bag is comfortable. Use the TOG guide supplied by the maker of your sleep sack, and check your baby's chest or the back of the neck.
Can I put a blanket over a sleep sack?
No. The Lullaby Trust says not to add extra blankets on top of a baby sleeping bag. If your baby feels cold, add a layer of clothing underneath or choose a higher tog.
Until what age can my baby use a sleep sack?
The AAP says sleep sacks that do not swaddle and let your baby move freely can be used as long as you want. Sacks that compress the arms and chest must stop once your baby shows signs of rolling.
Is a 2.5 tog sleep sack too warm?
It depends on the room, the clothes underneath and the product itself. The Lullaby Trust explains that materials and trapped air change warmth, which is why it does not publish a universal chart. Follow the maker's guide and check your baby regularly.
Sources
- The Lullaby Trust — How to dress your baby for sleep (room temperature and togs) checked October 13, 2026
- The Lullaby Trust — Your baby's room temperature checked October 13, 2026
- HealthyChildren.org (AAP) — Swaddling, is it safe for your baby? (wearable blankets and sleep sacks) checked October 13, 2026
- HealthyChildren.org (AAP) — How to keep your sleeping baby safe, AAP policy explained checked October 13, 2026
- The Lullaby Trust — How to choose baby sleeping products (safety standards) checked October 13, 2026
Mamavela explains; it does not replace your midwife, doctor or pediatrician, who know your situation. If something worries you, call them. In an emergency, call 911 (US), 999 (UK) or 112.