In hot weather, less is more: a short-sleeve bodysuit, a sun hat and shade. Sunshine makes it feel warmer than the number, so the app dresses lighter in sun and brings the sun hat in earlier.
What the app suggests on a sunny day, from the skin out, for a baby of 6–12 months:
23–35°C: short-sleeve bodysuit and sun hat. Hot — as little as possible, plus a sun hat and shade. 22°C: short-sleeve bodysuit, pants and sun hat. Warm — light single layers. 20–21°C: short-sleeve bodysuit, pants, socks and sun hat. Warm — light single layers.
Under six months, keep your baby out of direct sun altogether: shade first, and a wide-brim hat. The NHS says never to cover a pram with a muslin or blanket in the heat, because it traps the heat inside.
Overheating is the risk for a baby in the heat. Shade matters more than any garment, and the neck tells you most: warm but not sweaty is just right.
0–3 months, 28°C: short-sleeve bodysuit and sun hat. 3–6 months, 28°C: short-sleeve bodysuit and sun hat. 6–12 months, 28°C: short-sleeve bodysuit and sun hat. 1–3 years, 28°C: T-shirt, shorts and sun hat.
Never cover the pram with a muslin or blanket in the heat — it traps the heat.
Check the neck — warm but not sweaty means just right.