Warm rooms, on the other hand, can interrupt important sleep stages. REM sleep and slow-wave sleep—critical for recovery and memory—may be shortened. Heat can cause frequent waking and lighter sleep overall. A cooler room helps protect these vital stages.

Research also links cool sleeping environments to better metabolism and weight control. Cooler temperatures activate brown fat, which burns more calories. This may lower the risk of conditions like type 2 diabetes. Simple habits, like a warm bath before bed, can help you cool down and sleep better.