We developed a facile method for increasing the environmental stability of a tungsten bronze near-infrared (NIR)-absorbing window using tetraethyl orthosilicate (TEOS) and 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane (FDS). The environmental stability of the tungsten bronze NIR-absorbing window could be enhanced by applying a variety of protective layers (i.e., TEOS, fluoropolymer (CYTOP), FDS). The protective characteristics of each layer type are discussed. The protection of tungsten bronze surfaces by TEOS and FDS layers enormously enhanced the environmental stability of the NIR absorbing window, whereas an untreated tungsten bronze film rapidly lost its NIR absorption properties. The protection efficiency followed the order: TEOS/FDS>FDS>TEOS>CYTOP. The improved environmental stability arose from the closely packed structure of FDS, which can self-assemble on an oxide surface, such as the tungsten oxide or silicon oxide surfaces. The method developed here provides a simple, robust, and versatile way to improve the environmental stability of a NIR-absorbing window.