What tog sleeping bag for a south-facing bedroom in a UK summer?

Why can a south-facing room stay warm after a mild day?

Glass that faces the sun, a room under the roof, and a top-floor flat all store heat after the outdoor temperature has dropped. The forecast on your phone is not the air beside the cot. The Lullaby Trust says it is hard to guess, so use a thermometer in the room the baby sleeps in. Which? (11 June 2026) repeats the same 16–20°C target and notes how hard that band is in a heatwave, on holiday, or away from home.

A “summer 1.0 tog” chosen in May does not rewrite itself when the bedroom is still 23°C at 10pm. Measure this room, then open the bag’s table. The Lullaby Trust will not publish one clothing-and-tog chart for every product, because fabrics and trapped air differ.

How do I cool the sleep room before I pick a tog?

Official heat steps are about the room first, then clothing. They are the same for a south-facing bedroom, a loft conversion and a top-floor flat.

1. 1
   Shut out the daytime sun Lullaby Trust: keep curtains closed in the daytime so the room does not heat up as much. Which? says close blinds or curtains and keep cots out of direct sunlight.
2. 2
   Move the cot off the glass and the radiator Lullaby Trust and NHS: do not place the sleep space near a heat source or in direct sun. A south-facing sill is both.
3. 3
   Open the door and a window if you can do so without a fall risk Lullaby Trust wording is to open the bedroom door and a window if it is possible to do so without creating a hazard, so air can flow.
4. 4
   Use a fan on the room, not on the baby Lullaby Trust and Which?: a fan is fine to cool the room; do not aim it directly at the baby.
5. 5
   Read a thermometer at cot height Then — and only then — open the sleeping bag’s tog guide for that number. Check the baby’s chest or the back of the neck as well.

Which tog if the room is still above 20°C?

Use the table that came with that bag. NHS publishes typical commercial bands; they are a cross-check, not a replacement for the hangtag, and the Lullaby Trust will not lock every fabric to one chart.

The Lullaby Trust’s hot-weather page also says: check the baby sleep bag guidance for which tog to use. That means the bag in your hands, not the month on the calendar.

Does a loft or top-floor flat change the rule?

The rule does not change. Heat rises, so a loft or top-floor room is the same query family as a south-facing bedroom: the room can sit above the Lullaby Trust’s usual 16–20°C band after a sunny day. You still measure this sleep space at cot height, run the heat steps, then use the bag’s table. You do not pick tog from “it’s only June” or from a thermostat two floors down.

Which? also warns against waterproof mattress protectors that can make a baby sweat, and against covering a pram with a blanket that blocks airflow — useful on the same hot day, but this page is about the bedroom tog, not nursery policy or swaddling.

What if I cannot get the room below 20°C?

The Lullaby Trust says this is frustrating and common in hot weather. After lighter bedding, airflow, a fan aimed away, and closed daytime curtains, it is fine to have the baby in a short-sleeve vest or even just a nappy. Tommy’s midwife page uses the same nappy line, especially above 24°C. Keep following the rest of their safer-sleep advice: back, clear flat surface, no hat indoors, same room for the first six months.

Fluids stay on the NHS / Lullaby Trust side: fully breastfed babies may want to feed more and do not need extra water until solids; formula-fed babies may have a little cooled boiled water as well as milk feeds. That is not a tog decision.

In shortSouth-facing, loft and top-floor rooms need a thermometer, not a summer label. Cool the room with the official heat steps, read cot-level air, then use that bag’s tog table. If the room still will not drop, official pages allow a vest or a nappy.