Abstract Methods that allow polymer film to be carried out in a heterogeneous structure and scalable manner are highly desirable in materials science. Herein, a planar frontal polymerization (FP) strategy is presented that enables sustainable and scalable fabrication of heterogeneous films. Gravitational/buoyancy‐oriented assembly of optical microspheres ensures vertically graded photonic heterostructure. Meanwhile, FP eliminates the sustaining energy supply while achieving precise spatial immobilization of the heterostructure. The resultant films demonstrate structure and dimensional effects associated with optical responsiveness. It is shown that the heterogeneous film coupling with high‐crystallinity colloid photonic crystal exhibits high solar reflectance (), enhanced infrared emissivity () and tunable structural colors. Notably, the cooling performance of this colored hybrid coating surpasses that of most state‐of‐the‐art cooling designs with ≈7.0 °C sub‐ambient daytime cooling. Strikingly, this planar FP strategy offers feasibility and convenience for the scalable production of heterogeneous films, ensuring widespread applicability in industrialization for building envelopes.
Yu et al. (2026) studied this question.