An 18°C bedroom points to a 2.5 TOG sleeping bag as a starting point; at 22°C, look at 1 TOG instead. Check the particular bag’s clothing guide and your baby’s chest before deciding what goes underneath.
A sleeping bag leaves sleep-space rules unchanged
A sleeping bag keeps a baby covered without loose bedding riding over their face. It suits families who want that coverage, but it cannot make an unsafe sleep space safe or prevent SIDS. If a bag you own still fits and suits the room, you needn’t buy a winter-labelled replacement.
- Put your baby down on their back on a firm, flat, non-inclined cot or bassinet mattress, with their head and face uncovered.
- Keep pillows, duvets, bumpers, toys, nests and other soft items out of the sleep space.
- Keep the baby’s separate cot in the parents’ room for the first six months, as safer-sleep guidance recommends.
The overnight room temperature sets the TOG starting point
Measure where the baby sleeps with a room thermometer kept out of reach, and check whether the room changes overnight. TOG measures a bag’s insulation; it cannot tell you your baby’s final temperature. These ranges provide a shortlist. The particular bag’s dressing guide determines the next step.
| Sleep-room temperature | TOG starting point | What to check |
|---|---|---|
| Below 16°C | Some makers specify 3.5 TOG | Follow that bag’s exact clothing guide. If the room is markedly colder, especially for a newborn or vulnerable baby, address the room conditions and seek individual advice. |
| 16 to 20°C | 2.5 TOG in the NHS guide | Check the maker’s underlayers. An extra vest adds insulation. |
| 20 to 24°C | 1 TOG in the NHS guide | Use lighter clothing underneath toward the warmer end, following the maker’s guide. |
| 24 to 27°C | 0.5 TOG in the NHS guide | Some ranges offer 0.2 to 0.3 TOG. A baby may need little clothing underneath. |
| Above 27°C | No TOG prescription in the NHS table | A lightweight bodysuit or just a nappy can be appropriate in very hot weather. Monitor the baby and room; a bag may be unnecessary. |
The 16 to 20°C sleep-room recommendation is useful guidance, rather than an exact biological cutoff. A heated bedroom can call for a light bag even when it’s freezing outdoors. No NHS rule assigns 3.5 TOG to every room below 16°C.
Clothes underneath can make the chosen TOG too warm
Start with the clothing chart for the exact bag, then check your baby’s trunk. One maker pairs its 2.5 TOG bag with a sleepsuit at 16 to 20°C. For its 3.5 TOG bag, it specifies either a bodysuit or a sleepsuit at 14 to 16°C, then both below 14°C. Those combinations belong to those products; another bag can have different instructions.
- Feel the chest or back of the neck. Hands and feet commonly feel cooler and are a poor guide to adding a layer.
- If the chest or neck feels hot or sweaty, or hair is damp or skin flushed, remove a layer or use a lighter bag. Overheating is a safety concern.
- If the trunk feels cold, check the room and the maker’s chart, then adjust the clothing or bag. Check again if the room changes overnight.
A bag to grow into can let a baby slip inside
Choose within the maker’s weight and height limits, then fasten the bag on your baby. An age label such as “0 to 6 months” cannot establish a safe fit. The lower half should leave space for hips and knees to bend, while the neck and arm openings must stay secure.
- Check that the baby’s head cannot pass through the fastened neck opening and that their arms cannot disappear into the bag.
- Reject hoods, loose ties, insecure decorations and weighted bags. Leave the legs free to bend and move.
- Stop using an arms-in or body-compressing swaddle design as soon as the baby shows signs of trying to roll. An arms-free bag can continue if it fits.
Published minimums vary: one newborn bag starts at 3.2 kg, while premature-baby guidance says most bags can be used from around 4 kg, subject to their instructions. For a premature, small or medically vulnerable baby, ask the discharge team about fit and temperature needs before buying a larger bag to last longer.
Wash-day checks can catch a changing fit
Recheck the fastened openings after laundering and during use. A 2026 recall involved neck openings that could stretch enough to let a baby slip inside. An initially snug fit is no reason to stop checking.
- Fasten the shoulders and zip. Check that closures stay shut, the zip pull is secure, and stitching and filling remain contained. A bottom-opening zip can ease nappy changes; a zip guard keeps the fastening off skin.
- Read the care label before buying. Wash and drying instructions vary across cotton, filled and wool bags, so choose a routine you can follow.
- Check the maker’s claimed product standard and recalls alongside the bag itself. European cot-bag standard EN 16781:2026 was published in September 2026; a 2018 marking alone does not prove a bag defective.
A steady room favours a conventional bag
For a cot room that stays near 18°C, start by comparing correctly sized, sleeveless 2.5 TOG bags and their clothing guides. Choose a different design for a specific need:
- A convertible bag can serve a room with substantial temperature swings. Verify the TOG and dressing chart for each configuration, and secure every detachable part as instructed.
- A footed design can help an older mobile child move before or after bedtime. Check its neck fit and the maker’s cot-use instructions; stop using a cot bag if the child can climb out.
- Cotton, fleece, polyester-filled quilting and wool differ in feel and care. A fibre name, “breathable” claim or “four-season” label cannot replace the stated TOG and clothing guide.
Compare the price per correctly sized bag at the needed TOG, especially with multipacks. A second suitable bag helps while one is wet. If you find a discount, compare the same size, TOG, configuration and number of bags against their usual purchasable price; there’s no reliable best month to wait for.
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Extra blankets and winter hats create hazards
If your baby’s trunk feels cold, use a suitable bag or a maker-approved underlayer and recheck their warmth. Never put a blanket or duvet over a sleeping bag, and never stack bags to improvise extra insulation.
- Keep hats and hoods off for indoor sleep, and remove outdoor hats and extra clothing when you come inside.
- Keep the cot away from radiators and leave hot-water bottles out of the sleep space.
- Keep the baby’s head and face uncovered as you adjust their clothing or bag.
Frequently asked questions
Does a printed TOG prove a sleeping bag is safe?
No. A TOG label gives an insulation figure, not a safety approval. A targeted 2020 investigation found wide necks and inaccurate TOGs among sampled bags. It is not a current market failure rate, but it is a reason to check the seller, construction, instructions and recalls.
Can my baby wear a cot sleeping bag in a car seat?
Don’t put a bulky bag or insert between the baby and the fastened harness; it can compress in a crash and leave the straps loose. Use thin layers and, if needed, warmth over the harness while keeping the face clear. Move a sleeping baby to an appropriate flat sleep space when travel ends.
Can I use a blanket instead of buying a sleeping bag?
Some safer-sleep guidance permits a lightweight blanket instead of a bag if it is firmly tucked no higher than the shoulders, with the baby’s feet at the foot of the cot. Other guidance favours wearable clothing and a bare sleep space. Follow the safer-sleep guidance in your market; neither approach calls for a blanket over a bag.
How many sleeping bags should I buy?
One can be enough if it can be washed and dried before the next sleep. Two correctly fitting bags make leaks or slow drying easier to handle; frequent leaks or spit-up may justify a third. Match any spare to the room temperatures you actually have.
Will a sleeping bag prevent SIDS?
No product guarantees that. A bag’s practical benefit is keeping the baby covered without loose bedding that could reach the face. Back sleeping, a clear sleep space and avoiding overheating still matter.
How to choose
For most bedrooms that stay around 16 to 20°C, start with a correctly fitting, sleeveless 2.5 TOG bag. Use its own clothing guide, check your baby’s chest or neck, and change the combination if the room or your baby’s warmth changes. A reliably heated room may call for a lighter bag, even through winter.
This article was created using AI, following our team's editorial standards.
