Experimental determination of giant interfacial thermal resistance in thermally insulating hollow glass microspheres

Hollow glass microspheres (HGMs) are extensively employed in thermal insulation applications due to their remarkably low effective thermal conductivity. However, a detailed understanding of their thermal transport mechanism remains elusive. This study aims to provide in detail the thermal transport mechanism active in HGMs, particularly focusing on interfacial thermal resistance (ITR) in a wide temperature range (120 K to 300 K). For the first time, we experimentally extract the ITR between each HGMs by employing various size of particles. The measured value is around 0.0178 m²⸱K⸱W⁻¹ at room temperature and increases to 0.039 m²⸱K⸱W⁻¹ at 120 K. Our findings reveal that HGMs demonstrate substantially lower thermal conductivity than other insulation materials owing to their very high ITR. More than 80 % of solid heat conduction is contributed by means of ITR. These comprehensive measurements and thermal transport analyses provide critical insights into the design and development of advanced thermal insulation materials that can be realized through proper ITR designs.