Firewatch runs on the Unity game engine.[14] Ng disapproved of the tools for creating trees, and therefore hand-modeled the 23 kinds of trees that would be placed within the game 4,600 times. A custom shader was also employed to produce more stylized and simplified foliage.[15] The in-game fire lookout towers were built in accordance with government specifications, utilizing standard lumber size, after Ng's first attempt was unsatisfactory.[16]