Passive warm-keeping textiles could reduce carbon emissions by turning down indoor heating in winter. Polar bear hair exhibits a unique structure composed of a hollow core and an aligned porous shell, which extremely helps to resist heat transport. Great interest has arisen in the development of thermo-insulating textiles with this biomimetic structure. In this work, cellular hollow fibers were made by a large-scalable wet spinning-foaming process. This efficient method achieved rapid formation of polar bear hair-like fiber as well as facile turning properties of the fibers. The structure and properties of biomimetic fibers depended on the content of foaming agent. As-prepared porous thermoplastic polyurethane (TPU)/polyacrylonitrile (PAN) composited fiber showed excellent ductility. The maximum tensile strength and breaking elongation was 4.31 MPa and 121%, respectively. The corresponding woven textile exhibited excellent thermal insulation properties even under deformation by compression or tension. The temperature difference across the thickness of textile was 17.9 and 34.9°C under a background temperature of 0 and 80°C, respectively. It may pave the way to fabricate new structure–function integrated fiber materials for warm-keeping textiles.