Low-haze, transparent polymeric films for visual bidirectional passive thermal regulation

Highly transparent, low-haze polymeric films enabling bidirectional dynamic radiative heating and cooling hold significant promise for architectural and automotive applications; however, their development remains challenging. Herein, we present a low-haze, transparent polymeric film (LHTP) designed for visual regulation of bidirectional radiative heating and cooling. The LHTP film features a bilayer structure: a cooling layer comprising polydimethylsiloxane integrated with silicon dioxide aerogel microsphere of nanoparticles, and a heating layer fabricated via magnetron sputtering nanocoating of indium tin oxide onto a transparent polyethylene terephthalate substrate. The film achieves a high visible transmittance of 79.9% with a low haze of 15.4%, ensuring effective visual clarity. The heating side exhibits a low infrared emissivity of 44.5%, while the cooling surface demonstrates a high infrared emissivity of 90% alongside enhanced solar reflectance. Dynamic switching between heating and cooling modes is achieved via a simple flipping mechanism, yielding temperature increases of 8.6 °C and decreases of 6.9 °C, respectively. Furthermore, the LHTP film is mechanically flexible, exhibits dual-sided hydrophobicity, and possesses excellent Joule heating capability. Notably, it shows minimal performance degradation after one month of outdoor exposure. These properties collectively bolster its long-term potential for energy-efficient applications across building, automotive, and wearable eyewear technologies. A low-haze transparent polymeric film with a bilayer hierarchical structure enables dynamic passive radiative heating and cooling, achieving high visible transmittance under low haze, efficient temperature regulation, flexibility, and outdoor durability for energy-saving applications.