A Small-Size Cross-Over Trial of Heating Pad Use during Winter on Sleep

¹ Center for the Built Environment, University of California, Berkeley, CA, USA
² School of Architecture and Planning, Hunan University, Changsha, China
³ ES Air Solution R&D Lab, LG Electronics, Seoul, Republic of Korea
⁴ Department of The Built Environment, National University of Singapore, Singapore
⁵ Department of Architecture, University of California, Berkeley, CA, USA
⁶ Department of Civil and Environmental Engineering, University of California, Berkeley, CA, USA

Abstract

Sleep quality is a key determinant of physical health, mental well-being, and cognitive performance, yet the studies of the influence of indoor environmental factors on sleep in real-world settings remain insufficient. While laboratory experiments have highlighted the effects of individual parameters like temperature, CO₂, particulate matter, and noise on sleep, multi-parameter field studies combining environmental, physiological, and subjective data are scarce. To address this gap, we conducted a pilot study with five participants (aged 20-31) to evaluate bedroom environmental conditions, their relationship to sleep quality, and the potential role of a heating pad as a thermal intervention in winter. This within-subject weekly crossover study consisted of two phases (3 weeks each): an observational/control phase, during which participants' bedrooms were monitored without intervention, and an intervention phase introducing the use of an electrical heating pad. Environmental variables (temperature, CO₂, PM2.5, sound pressure level) were continuously measured alongside physiological signals from wearables (heart rate, sleep parameters). Subjective sleep quality and thermal perception were assessed daily using Cozie, an open-source Apple Watch survey tool. Results revealed substantial variability in environmental conditions between bedrooms, with CO₂ levels frequently exceeding recommended thresholds, typical night-time temperatures fluctuating by 3 K within a bedroom, between 16 - 22 °C across homes, and notable differences in sound pressure level exposure. The heating pad intervention improved subjective thermal comfort for most participants and was linked to modest improvements in self-reported sleep quality, although inter-individual responses varied. Our findings highlight the importance of considering multiple indoor environmental factors in relation to sleep and emphasize the potential of targeted thermal interventions to improve sleep quality. However, since the small sample size and short cross-over intervention period (3 weeks per condition) limit the generalizability of the results, future studies with larger and more diverse cohorts are needed to disentangle the relative contributions of environmental and physiological factors, and to assess the long-term efficacy of heating pads and other interventions in improving sleep quality.