At 2°C outside, your bedroom could drop below 14°C by morning — the point where cold itself starts disrupting sleep. The risk isn't discomfort (a thick duvet handles that), it's waking in the early hours as your body diverts energy to stay warm.

Dew point is just 5°C — dry, fresh air. This is the kind of night where an open window does exactly what you want it to: brings in cool, comfortable air that helps your body maintain its natural overnight temperature drop.

A 5.7°C drop between bedtime and 4am is substantial. This natural cooling aligns with your circadian rhythm — your body temperature dips in the early hours, and the environment cooling alongside it produces the deepest sleep of the night.