Infrared stealth and energy saving of the hydroglass. (a) The transmittance results of the double PE slides, double PE slides with water interlayer (water window), and HNAH window in the IR band. (b) The IR transmittance results of the HNAH window at 40°C and after 10-cycle heating. (c) The thermal infrared photographs of a naked human hand (left), the hand covered by water window (middle), and the hand covered by the HNAH window (right). The insert photographs are the water window and the HNAH window, respectively. (d) Schematic illustration of a model chamber with different window materials. (e) Temperature profiles of the thermometer inside the model chamber with double PE slides or HNAH as the window materials. (f) Cyclic temperature tests recorded by the thermometer inside the model chamber with different window materials.