<p>Heating-cooling cycle tests.</p>

However, the thermochromic performance of coatings under a spatially separated heat source, as well as the influence of coating parameters on thermochromic behavior, remains insufficiently explored. In this study, an earplug structure embedded with a thermochromic coating was prepared, and the effects of coating filler content, coating thickness, and dye concentration on thermochromic behavior were systematically investigated.

A distinct color transition was successfully achieved even when the coating was positioned away from the heat source. Simulation results indicate that, under a 40 °C heat source, the effective color‑transition temperature of the coating within the earplug structure should be maintained at approximately 34 °C. The incorporation of HBN accelerates the transition process and narrows the color-transition temperature range, enabling complete color change at around 34 °C. In addition, the effective color-changing distance is extended from 2.2 cm to 3.7 cm; however, a high HBN content reduces the color difference.