Scalable fabrication of super-elastic TPU membrane with hierarchical pores for subambient daytime radiative cooling

Passive radiative cooling materials (PRCMs) has arose widespread concern with the advantage of cooling a surface by radiating heat to the cold outer space and reflecting sunlight. However, the cooling effect sharply deteriorated in the stretching state. Besides, widespread reflectivity within visible light (VIS) and near-infrared (NIR) range remained a huge challenge for the structure design. Herein, we proposed a porous thermoplastic urethanes (TPU) membrane with a high thermal emissivity of 95% and a sunlight reflectivity of 93%. Abundant hierarchical pores with submicro and micro sizes generate when the solvent of the TPU sol is exchanged by water, which tremendously strengthens the sunlight-reflecting behavior of the porous TPU membrane, especially in the NIR region. By covering the porous TPU membrane on the top, the temperature of the substrate, model house, and hood of the car cool up to 8.8, 16.3, and 18.0 °C, respectively, compared to the bare state. Moreover, the porous TPU membrane shows outstanding elastic cooling properties that the damage of IR emissivity and sunlight reflectivity was minimal even in a tensile strain of 450%.