Bedroom thermal conditions and their impacts on sleeping thermal comfort, sleep quality, and next‑day wakefulness

The thermal environment during sleep influences sleep quality, yet real-world evidence linking bedroom conditions, subjective thermal comfort, and sleep outcomes remains limited. This one-week field study followed 33 healthy university students in Hong Kong dormitories during early to mid-summer to examine how bedroom thermal conditions and adaptive bedding behavior relate to thermal sensation, satisfaction, and sleep. Higher bedroom temperatures were associated with warmer thermal sensation votes (TSV), greater thermal dissatisfaction, and poorer self-reported sleep quality. Minimum dissatisfaction occurred at TSV ≈ -0.57 and ∼24-24.6°C. Participants primarily adapted via bedding insulation and coverage; females selected higher insulation and reported lower dissatisfaction at cooler sensations. Mixed-effects models identified air temperature as the dominant predictor of both TSV and satisfaction, with bedding insulation exerting additional, temperature-dependent effects. A significant temperature-insulation interaction indicated that the impact of insulation on warmth sensation and satisfaction changed with ambient temperature, demonstrating that sleeping thermal comfort depends on their combined influence rather than temperature alone. The model also revealed significant gender effects on TSV, and the impact of clothing differed between males and females. Cooler sensations were linked to better self-reported sleep, whereas device-derived sleep metrics showed weaker and less consistent associations with temperature. Enabling adaptive bedding may help minimize dissatisfaction and support better perceived sleep. Improved thermal satisfaction from one night to the next resulted in modestly lower next-day sleepiness at selected time points. These findings support an optimal, slightly cool sensation for summer sleep in real bedrooms (approximately 23-25°C) and provide predictive models incorporating temperature-insulation interactions.