0.5 tog sleeping bag or just a nappy in a UK heatwave?

What do official UK pages say when the room will not cool?

Lullaby Trust, Which? and Tommy's all start with the room, then strip layers. None of them own the search "0.5 tog versus nappy". They do all say that once you have done the cooling steps and the sleep-space still will not sit at 16–20°C, a short-sleeve vest or nappy-only is fine.

Brand summer guides often sell 0.5 tog as the answer. The official pages sell lighter layers after you have cooled the room. A 0.5 tog bag still has to fit at the shoulders, and NHS still says there should be no other bedding with a bag.

Where does 0.5 tog sit on the NHS list?

NHS lists 0.5 tog for hot weather and warm rooms of 24 to 27°C. The same page lists 1.0 tog for 20–24°C and 2.5 tog for 16–20°C. Clothing can be adjusted with the room and the tog. A bag used in that 24–27°C band is still a sleeping bag: NHS wants a close shoulder fit so the head cannot slip down inside, and no extra blankets.

Nappy-only is not on the NHS tog table because it is not a commercial tog. It sits on the Lullaby Trust / Which? / Tommy's heatwave pages as the last clothing step when the room stays hot. Tommy's names above 24°C as the point where nappy-only is an option they are comfortable stating.

How do I cool the room before I choose 0.5 tog or a nappy?

Official heatwave steps are almost the same list on Lullaby Trust, Which? and Tommy's. Do these before you treat the bag as the problem.

1. 1
   Stop the room storing heat Keep curtains or blinds closed in the daytime. Lullaby Trust and Which? both treat daytime sun on the glass as the reason a UK bedroom is still 25°C at 10pm.
2. 2
   Move air, if you can do it without a fall risk Open the bedroom door and a window when that does not create a security or fall hazard. Tommy's adds: as many windows as you can, with curtains partly closed against direct sun.
3. 3
   Use a fan on the room, not the baby Lullaby Trust and Which?: a fan is fine; do not aim it directly at the baby. Which? and Tommy's mention a bowl of ice or a frozen bottle in front of the fan as a way to cool the air that moves.
4. 4
   Read a thermometer at cot height Lullaby Trust: it is hard to guess. If the room is still 24–27°C, NHS's 0.5 tog band applies to a commercial bag. If it is still hotter than you can bring down, the charity pages allow vest or nappy-only.
5. 5
   Choose the lighter option on the label in front of you If you keep a bag on, use the clothing table for that 0.5 tog product. If you take the bag off, Which? says no covers either. Feel the chest or the back of the neck after they have been down for a stretch.

How do I tell if they are too hot, with or without a bag?

The check does not change because you picked nappy-only. Lullaby Trust and Tommy's: feel the chest or the back of the neck. Hands and feet usually feel cooler, which is normal. Hot, clammy or sweaty skin is the cue to remove a layer and to keep working on the room.

• Which? also flags flushed cheeks and sweat around the hairline as signs the baby has warmed up in sleep.
• Waterproof mattress protectors can hold heat. Which? and Tommy's both say to avoid them in hot weather if you can.
• Hats stay off indoors. Lullaby Trust: babies lose heat through the head.
• Do not cover a pram with a blanket to make shade. Lullaby Trust: that traps heat and hides the baby. Use a clip-on sunshade or parasol instead. That is a daytime note, not a cot note.

Does a heatwave change milk and water, or only the bag?

The bag is only one lever. Lullaby Trust and Tommy's: fully breastfed babies do not need extra water until they start solids, but they may want to feed more. Formula-fed babies can have a little cooled boiled water as well as usual milk feeds; Tommy's says keep that modest and not just before a feed. Which? matches the cooled-boiled-water rule for bottle-fed babies under six months.

In shortCool the room first. NHS places 0.5 tog at 24–27°C. Lullaby Trust, Which? and Tommy's all allow a short-sleeve vest or nappy-only when that room will not come down. Feel the chest. MayTally does not crown 0.5 tog or nappy-only as the heatwave winner.