Facile Fabrication of Light‐Colored Polyethylene Terephthalate/Cesium Tungsten Bronze Fibers With Photothermal Conversion, Enhanced Thermal Insulation, and Excellent Cationic Dyeability

Light‐colored, dyeable, and thermally insulating fibers with efficient photothermal conversion are desirable for cold‐weather protective textiles. Herein, polyethylene terephthalate (PET) was melt‐spun with cesium tungsten bronze (Cs 0.33 WO 3 , 0.4 wt%) and two water‐soluble polyesters (WSPs) of low and high intrinsic viscosity to produce “A”‐shaped hollow fibers. Alkaline weight reduction generated 1–2 μm surface pits while preserving SO 3 − dye sites in the fiber bulk, yielding a tensile strength of 2.74 cN/dtex. Combined surface pitting and the “A”‐shaped cross‐section suppressed specular reflectance to produce a matte appearance. Under 600 W m −2 xenon irradiation for 10 min, the fabric achieved an equilibrium temperature rise of 36.8°C, exceeding that of neat PET by 7.1°C. When placed on a 37°C hot plate for 10 min, the fabric exhibited a temperature drop approximately 1.0°C smaller than that of neat PET, indicating enhanced thermal insulation. The fibers were dyeable with cationic dyes under atmospheric pressure, and the resulting fabric exhibited a 14% higher wicking height than the control. This one‐step melt‐spinning approach offers a scalable route to lightweight PET fibers integrating photothermal heating, passive insulation, and cationic dyeability for thermal‐protective applications.