<p>Traditional post-treatment with microencapsulated phase change materials (MPCMs) typically results in poor MPCM distribution and weak adhesion to fabric surfaces. In this study, we applied a novel yarn-level impregnation method, chemically treating kapok-blended yarns and impregnating them with MPCM solution (n-octadecane core/polyurea shell; phase-change temperature: 301.15 K, latent heat: 1.90 × 10⁵ J·kg⁻¹) before weaving to penetrate hollow cavities and interstitial spaces. This approach significantly enhances the loading capacity and thermal regulation performance of the fabric. The results showed that the yarn-level impregnation method achieved a higher MPCM content (13.9%) and better washing durability (91.01% mass retention rate) compared to the traditional post-treatment method (8.8% MPCM content and 81.89% mass retention rate). Additionally, a numerical model incorporating conduction, convection, radiation and phase transition through a computational fluid dynamics approach was developed to analyze the comparative heat transfer process. Good agreement was achieved between the experiment and simulation, with relative errors in surface temperature of 2.72% for fabrics without thermal regulation and 1.20% for fabrics with thermal regulation. Then the effect of various parameters including fabric thickness, ambient temperature and wind speed on heat transfer was further analyzed. Simulation results indicated that thicker fabrics improved thermal insulation and extended the heat-release period of MPCMs, whereas reduced ambient temperatures and elevated wind speeds hastened cooling and curtailed the phase-change interval. This study provides a novel and effective approach for developing high-performance phase-change thermal-regulating textiles and offers theoretical insights into optimizing their thermal regulation performance.</p>