Reduced-scale Hot Box design and validation for rapid thermal conductivity evaluation of insulating materials

Thermal insulation research requires experimental tools capable of accurately characterizing materials while adapting to the constraints of laboratory-scale development, such as small samples and the need for rapid testing. One versatile method to determine thermal properties is the Hot Box (HB) method, consisting of hot and cold isolated chambers separated by a wall in which the material under characterization is located. However, conventional HB systems are typically designed for standard compliance and large-scale building components, requiring large specimens and long steady-state cycles. In this work, a reduced-scale, low-cost Hot Box prototype was designed and validated, specifically optimized for reduced specimen dimensions and accelerated testing. The system enables reliable thermal conductivity measurements using rigid specimens as small as 15 × 15 cm 2 and 1-4 cm thick, while maintaining relative errors below 4% after calibration. Furthermore, the steady-state measurement time was reduced to 3 h, significantly shorter than typical HB cycles, and further analysis demonstrated the feasibility of shortening the cycle to below 1 h without compromising accuracy. Infrared thermography confirmed that the effective measurement area remains unaffected by edge thermal bridges, supporting the validity of reduced sample dimensions. Finally, the developed Hot Box was used to simulate dynamic conditions taking advantage of the prototype design, showing its versatility and its research applications. The proposed design provides a compact and time-efficient alternative to conventional HB systems, particularly suited for the evaluation of emerging insulating materials produced at laboratory scale. • Desing, construction, calibration, and validation of a reduced-scale Hot Box. • Analysis of steady-state and dynamic thermal conductivity properties of insulating materials. • Deviations under 3% in terms of thermal conductivity are obtained for samples with thickness lower than 4 cm. • The surface dimension of the samples can be at least as low as 15 × 15 cm 2 and the measurement time as low as 3h.